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 12 Months Ended
Mar. 31, 2018
Mar. 31, 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    
Other comprehensive income before reclassifications (161) 6  
Amounts reclassified from accumulated OCI to earnings 13 4  
Period change   10  
Balance, end of period 11,308 10,437 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 (161) 7  
Amounts reclassified from accumulated OCI to earnings 12 4  
Period change (149) 11  
Balance, end of period (428) (182) (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 (1)  
Amounts reclassified from accumulated OCI to earnings 0 0  
Period change 0 (1)  
Balance, end of period 0 (4) 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 1 0  
Period change 1 0  
Balance, end of period (249) (205) (250)
Accumulated Other Comprehensive Loss      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period (528) (401) (401)
Period change (148)    
Balance, end of period (677) (391) (528)
Reclassification out of Accumulated Other Comprehensive Income      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Net unrealized loss on securities transfer $ (147) $ 81 $ (95)