Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance			$ 2,598
Changes in Level 3, ending balance	2,676		2,598
Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance			82
Changes in Level 3, ending balance	42		82
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	12,092	11,261
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	15	13
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	236	85
Purchases	491	787
Sales	(138)	(4)
Settlements	(730)	(719)
Transfers into Level 3	0	533
Transfers out of Level 3	(7,335)	(364)
Changes in Level 3, ending balance	4,631	11,592
Net change in unrealized gains (losses) relating to instruments still held	0	9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Derivatives Assets And Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	37	20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	3
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	2	0
Purchases	(1)	(1)
Sales	0	0
Settlements	0	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	(1)	0
Changes in Level 3, ending balance	37	21
Net change in unrealized gains (losses) relating to instruments still held	0	9
Cash Accruals Not Included In Schedule Assets Measured For Fair Value On Recurring Basis	10	6
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Retained Interest [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	17	21
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	1	1
Sales	0	0
Settlements	(1)	(2)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Changes in Level 3, ending balance	17	20
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Assets And Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance		279
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income		0
Purchases		0
Sales		0
Settlements		0
Transfers into Level 3		0
Transfers out of Level 3		(279)
Changes in Level 3, ending balance		0
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Domestic Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	3,128	2,918
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	8	8
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	61	63
Purchases	92	153
Sales	(18)	(2)
Settlements	(36)	(112)
Transfers into Level 3	0	96
Transfers out of Level 3	(23)	(53)
Changes in Level 3, ending balance	3,212	3,071
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	578	96
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	27
Purchases	7	9
Sales	(31)	0
Settlements	(2)	(7)
Transfers into Level 3	0	435
Transfers out of Level 3	0	0
Changes in Level 3, ending balance	552	560
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	16	86
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	5	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(4)	(1)
Purchases	0	0
Sales	(14)	0
Settlements	0	(4)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Changes in Level 3, ending balance	3	81
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	9	10
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	0	0
Sales	(7)	0
Settlements	0	(1)
Transfers into Level 3	0	2
Transfers out of Level 3	0	0
Changes in Level 3, ending balance	2	11
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	7,575	6,898
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	1
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	160	(27)
Purchases	140	405
Sales	(11)	0
Settlements	(442)	(369)
Transfers into Level 3	0	0
Transfers out of Level 3	(7,310)	0
Changes in Level 3, ending balance	112	6,908
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Foreign Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	455	666
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	1
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(7)	14
Purchases	252	220
Sales	(57)	(2)
Settlements	(245)	(223)
Transfers into Level 3	0	0
Transfers out of Level 3	(1)	0
Changes in Level 3, ending balance	397	676
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Foreign Government Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	2	31
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(30)
Changes in Level 3, ending balance	2	1
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	266	225
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	26	9
Purchases	0	0
Sales	0	0
Settlements	(1)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(2)
Changes in Level 3, ending balance	291	232
Net change in unrealized gains (losses) relating to instruments still held	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	9	11
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	2	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(2)	0
Purchases	0	0
Sales	0	0
Settlements	(3)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Changes in Level 3, ending balance	6	11
Net change in unrealized gains (losses) relating to instruments still held	$ 0	$ 0