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, 2019
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance, beginning of period $ 11,102 $ 10,814 $ 10,814  
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets   1    
Other comprehensive income before reclassifications 150 (161)    
Amounts reclassified from accumulated OCI to earnings 4 13    
Period change 154 (148)    
Balance, end of period 11,432 11,308 11,102  
Unrealized gains and (losses) on debt securities | Debt Securities        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance, beginning of period (363) (278) (278)  
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets       $ (1)
Other comprehensive income before reclassifications 143 (161)    
Amounts reclassified from accumulated OCI to earnings 3 12    
Period change 146 (149)    
Balance, end of period (217) (428) (363)  
AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] | Equity Securities [Member]        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance, beginning of period 0      
Other comprehensive income before reclassifications 7      
Amounts reclassified from accumulated OCI to earnings 0      
Period change 7      
Balance, end of period 7   0  
Unrealized gains (losses) for pension and other post- retirement obligations        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance, beginning of period (246) (250) (250)  
Other comprehensive income before reclassifications 0 0    
Amounts reclassified from accumulated OCI to earnings 1 1    
Period change 1 1    
Balance, end of period (245) (249) (246)  
Accumulated Other Comprehensive Loss        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance, beginning of period (609) (528) (528)  
Balance, end of period (455) (677) (609)  
Reclassification out of Accumulated Other Comprehensive Income        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Net unrealized loss on securities transfer $ (134) $ (147) $ (137)