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
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period     $ 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 (218) $ 42  
Amounts reclassified from accumulated OCI to earnings 17 9  
Period change   51  
Balance, end of period 11,472 10,654 10,814
Unrealized gains and (losses) on debt securities | Debt Securities      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period     (193)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets (1)    
Other comprehensive income before reclassifications (218) 42  
Amounts reclassified from accumulated OCI to earnings 15 7  
Period change (203) 49  
Balance, end of period (482) (144) (278)
Unrealized gains and (losses) on cash flow hedging derivatives      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period     (3)
Other comprehensive income before reclassifications 0 0  
Amounts reclassified from accumulated OCI to earnings 0 1  
Period change 0 1  
Balance, end of period 0 (2) 0
Unrealized gains (losses) for pension and other post- retirement obligations      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period     (205)
Other comprehensive income before reclassifications 0 0  
Amounts reclassified from accumulated OCI to earnings 2 1  
Period change 2 1  
Balance, end of period (248) (204) (250)
Accumulated Other Comprehensive Loss      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period     (401)
Period change (201)    
Balance, end of period (730) (350) (528)
Reclassification out of Accumulated Other Comprehensive Income      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Net unrealized loss on securities transfer $ (144) $ 98 $ (95)