v3.8.0.1
Derivative Instruments (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Sep. 14, 2017
Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
Total derivative assets $ 1,205 $ 1,367    
Total derivative liabilities 643 345    
Anticipated pre-tax loss reclassified from accumulated other comprehensive income (loss) to earnings $ 157      
Maximum Length of Time Hedged in Cash Flow Hedge (future cash flows) 5 years      
Maximum Length of Time Hedged in Cash Flow Hedges (existing cash flows) 40 years      
Net investment hedges income (loss) before taxes $ 526 536   $ 541
Derivative [Line Items]        
Notional of credit derivative 0 500    
Fair value of credit derivative liability 0 17    
Credit protection derivatives outstanding notional amounts 178 256    
Purchased credit protection, Liability 5 8    
Single Name        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 114 112    
Fair value asset (liability) $ 2 1    
Credit Derivatives Written Max Length Of Maturities (less than) 3 years      
Single Name | NAIC 1        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted $ 36      
Single Name | NAIC 2        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 62      
Single Name | NAIC 3        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 5      
Single Name | NAIC 4        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 2      
Single Name | NAIC 5        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 5      
Single Name | NAIC 6        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 4      
Credit Default Index        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted 1,022 50    
Fair value asset (liability) $ 18 $ (1)    
Credit Derivatives Written Max Length Of Maturities (less than) 30 years      
Credit Default Index | NAIC 1        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted $ 52      
Credit Default Index | NAIC 4        
Derivative [Line Items]        
Credit Derivative, Maximum Exposure, Undiscounted $ 970      
Subordinated Debt [Member] | Subsidiaries | Other Credit Derivatives [Member]        
Derivative [Line Items]        
Termination Loans     $ 12