Fair Value Measurements (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cumulative Gain (Loss) Adjustment For Non Performance Risk	$ 1	$ 16
Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	39,168	41,090
Liabilities	1,573	1,718
Fair Value Of Securities Transferred Between Level 1 And Level 2	0
Recurring | Derivative liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	503	540
Recurring | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	1,070	1,178
Recurring | Retained interest
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets		0
Recurring | Derivatives
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	2,003	2,413
Recurring | Other Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	233	277
US Corporate | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	22,902	23,715
State and municipal | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	4,340	4,675
Residential Mortgage Backed Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	984	1,692
Commercial mortgage backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	2,405	3,063
Asset-backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	97	295
Corporate - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	868	1,017
Fair Value Of Securities Transferred Between Level 1 And Level 2		13
Government - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	1,252	1,710
Fair Value Of Securities Transferred Between Level 1 And Level 2		487
U.S. Government and federal agency | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	3,882	2,013
Available-for-sale Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	185	199
Trading | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	19	21
Level 1 | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	197	192
Liabilities	0	0
Level 1 | Recurring | Derivative liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Level 1 | Recurring | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Level 1 | Recurring | Retained interest
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets		0
Level 1 | Recurring | Derivatives
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | Recurring | Other Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | US Corporate | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | State and municipal | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | Residential Mortgage Backed Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | Commercial mortgage backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | Asset-backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | Corporate - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	6	0
Level 1 | Government - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	14	0
Level 1 | U.S. Government and federal agency | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 1 | Available-for-sale Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	159	171
Level 1 | Trading | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	19	21
Level 2 | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	41,505	44,232
Liabilities	6,227	6,068
Level 2 | Recurring | Derivative liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	5,156	4,890
Level 2 | Recurring | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	1,070	1,178
Level 2 | Recurring | Retained interest
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets		0
Level 2 | Recurring | Derivatives
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	8,545	9,957
Level 2 | Recurring | Other Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 2 | US Corporate | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	19,853	20,659
Level 2 | State and municipal | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	4,259	4,560
Level 2 | Residential Mortgage Backed Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	981	1,676
Level 2 | Commercial mortgage backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	2,403	3,054
Level 2 | Asset-backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	59	172
Level 2 | Corporate - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	579	680
Level 2 | Government - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	1,238	1,708
Level 2 | U.S. Government and federal agency | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	3,573	1,747
Level 2 | Available-for-sale Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	15	19
Level 2 | Trading | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 3 | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	4,086	4,250
Liabilities	5	13
Level 3 | Recurring | Derivative liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	5	13
Level 3 | Recurring | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Level 3 | Recurring | Retained interest
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets		0
Level 3 | Recurring | Derivatives
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	79	40
Level 3 | Recurring | Other Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	233	277
Level 3 | US Corporate | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	3,050	3,056
Level 3 | State and municipal | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	81	115
Level 3 | Residential Mortgage Backed Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	2	16
Level 3 | Commercial mortgage backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	1	9
Level 3 | Asset-backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	38	123
Level 3 | Corporate - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	283	337
Level 3 | Government - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	2
Level 3 | U.S. Government and federal agency | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	309	266
Level 3 | Available-for-sale Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	10	9
Level 3 | Trading | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	(6,620)	(7,584)
Liabilities	(4,658)	(4,363)
Netting Adjustment | Recurring | Derivative liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	(4,658)	(4,363)
Netting Adjustment | Recurring | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Netting Adjustment | Recurring | Retained interest
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets		0
Netting Adjustment | Recurring | Derivatives
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	(6,620)	(7,584)
Netting Adjustment | Recurring | Other Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | US Corporate | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | State and municipal | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Residential Mortgage Backed Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Commercial mortgage backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Asset-backed | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Corporate - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Government - non-U.S. | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | U.S. Government and federal agency | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Available-for-sale Securities | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Trading | Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	$ 0	$ 0