Derivatives (Cash Flow Hedges) (Details) - Cash Flow Hedges [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivatives in cash flow hedging relationships
Amount of Gains (Losses) Deferred in AOCI (Effective Portion)	$ (7)	$ 800	$ 203	$ 1,496
Interest rate swaps
Derivatives in cash flow hedging relationships
Amount of Gains (Losses) Deferred in AOCI (Effective Portion)	73	140	78	353
Foreign currency swaps
Derivatives in cash flow hedging relationships
Amount of Gains (Losses) Deferred in AOCI (Effective Portion)	(174)	622	(13)	1,096
Credit forwards [Member]
Derivatives in cash flow hedging relationships
Amount of Gains (Losses) Deferred in AOCI (Effective Portion)	0	0	0	0
Interest rate forwards
Derivatives in cash flow hedging relationships
Amount of Gains (Losses) Deferred in AOCI (Effective Portion)	94	38	138	47
Net derivative gains (losses)
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	423	(249)	645	69
Amount and Location of Gains (Losses) Recognized In Income (Loss) on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	4	5	7	2
Net derivative gains (losses) | Interest rate swaps
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	6	18	14	28
Amount and Location of Gains (Losses) Recognized In Income (Loss) on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	6	1	7	0
Net derivative gains (losses) | Foreign currency swaps
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	414	(269)	632	37
Amount and Location of Gains (Losses) Recognized In Income (Loss) on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(1)	4	1	2
Net derivative gains (losses) | Credit forwards [Member]
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	1	3	1	3
Amount and Location of Gains (Losses) Recognized In Income (Loss) on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0	0
Net derivative gains (losses) | Interest rate forwards
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	2	(1)	(2)	1
Amount and Location of Gains (Losses) Recognized In Income (Loss) on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(1)	0	(1)	0
Net Investment Income
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	5	5	11	9
Net Investment Income | Interest rate swaps
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	4	4	9	7
Net Investment Income | Foreign currency swaps
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	(1)	(1)	(1)	(1)
Net Investment Income | Credit forwards [Member]
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	0	0	0	0
Net Investment Income | Interest rate forwards
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	2	2	3	3
Other expenses
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	1	1	2	2
Other expenses | Interest rate swaps
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	0	0	0	0
Other expenses | Foreign currency swaps
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	0	0	1	1
Other expenses | Credit forwards [Member]
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	0	0	0	0
Other expenses | Interest rate forwards
Derivatives in cash flow hedging relationships
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	$ 1	$ 1	$ 1	$ 1