Quarterly report pursuant to Section 13 or 15(d)

OTHER COMPREHENSIVE INCOME OTHER COMPREHENSIVE INCOME - AOCI Roll Forward (Details)

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OTHER COMPREHENSIVE INCOME OTHER COMPREHENSIVE INCOME - AOCI Roll Forward (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]          
Balance, beginning of period     $ 10,814 $ 10,308 $ 10,308
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets $ 1   1    
Other comprehensive income before reclassifications     (281) 17  
Amounts reclassified from accumulated OCI to earnings     20 14  
Period change     (261) 31  
Balance, end of period 10,934 $ 10,699 10,934 10,699 10,814
Unrealized gains and (losses) on debt securities | Debt Securities          
AOCI Attributable to Parent, Net of Tax [Roll Forward]          
Balance, beginning of period     (278) (193) (193)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets         (1)
Other comprehensive income before reclassifications     (281) 15  
Amounts reclassified from accumulated OCI to earnings     17 12  
Period change     (264) 27  
Balance, end of period (543) (166) (543) (166) (278)
Unrealized gains and (losses) on cash flow hedging derivatives          
AOCI Attributable to Parent, Net of Tax [Roll Forward]          
Balance, beginning of period     0 (3) (3)
Other comprehensive income before reclassifications     0 2  
Amounts reclassified from accumulated OCI to earnings     0 0  
Period change     0 2  
Balance, end of period 0 (1) 0 (1) 0
Unrealized gains (losses) for pension and other post- retirement obligations          
AOCI Attributable to Parent, Net of Tax [Roll Forward]          
Balance, beginning of period     (250) (205) (205)
Other comprehensive income before reclassifications     0 0  
Amounts reclassified from accumulated OCI to earnings     3 2  
Period change     3 2  
Balance, end of period (247) (203) (247) (203) (250)
Accumulated Other Comprehensive Loss          
AOCI Attributable to Parent, Net of Tax [Roll Forward]          
Balance, beginning of period     (528) (401) (401)
Balance, end of period (790) (370) $ (790) $ (370) (528)
Reclassification out of Accumulated Other Comprehensive Income          
AOCI Attributable to Parent, Net of Tax [Roll Forward]          
Net unrealized loss on securities transfer $ (141) $ 97     $ (95)