Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	$ 2,875		$ 2,875
Net change in unrealized gains (losses) relating to instruments still held	0
Domestic Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	3,372	3,096	3,372	3,096	3,251	3,235	3,119	3,198
Net realized/unrealized gains (losses) included in earnings	33	14	59	101
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(71)	3	(34)	(20)
Purchases	119	30	132	75
Sales	(40)	(41)	(71)	(155)
Settlements	(31)	(29)	(47)	(103)
Transfers into Level 3	116	0	116	0
Transfers out of Level 3	(5)	0	(18)	0
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	97	45	97	45	107	41	118	66
Net realized/unrealized gains (losses) included in earnings	0	0	(3)	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	(2)	3	1
Purchases	0	1	0	2
Sales	0	0	0	(4)
Settlements	(2)	0	(3)	(1)
Transfers into Level 3	1	0	69	71
Transfers out of Level 3	(9)	(72)	(10)	(90)
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	0	7	0	7	1	4	11	49
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	1	0	1
Purchases	0	(1)	0	6
Sales	(1)	0	(1)	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	3
Transfers out of Level 3	0	(4)	(3)	(52)
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	81	209	81	209	79	77	210	225
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	1	0	3	(5)
Purchases	1	0	1	4
Sales	0	0	0	0
Settlements	0	(1)	0	(4)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	(11)
Net change in unrealized gains (losses) relating to instruments still held		0	0	0
Foreign Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	1,363	1,537	1,363	1,537	1,249	1,204	1,479	1,486
Net realized/unrealized gains (losses) included in earnings	(3)	(1)	(12)	(28)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(63)	28	(3)	82
Purchases	306	0	316	12
Sales	0	0	0	(28)
Settlements	(52)	(31)	(78)	(60)
Transfers into Level 3	9	62	23	73
Transfers out of Level 3	(83)	0	(87)	0
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	4,304	3,132	4,304	3,132	4,404	4,040	2,826	2,540
Net realized/unrealized gains (losses) included in earnings	7	(3)	3	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(89)	(19)	(47)	55
Purchases	57	409	398	780
Sales	(75)	(43)	(106)	(152)
Settlements	0	(1)	0	(11)
Transfers into Level 3	0	0	16	1
Transfers out of Level 3	0	(37)	0	(81)
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Foreign Government Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	51	274	51	274	52	84	162	156
Net realized/unrealized gains (losses) included in earnings	0	(16)	(34)	(16)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	8	35	14
Purchases	13	13	65	13
Sales	(1)	0	(72)	0
Settlements	(13)	0	(27)	0
Transfers into Level 3	0	107	0	107
Transfers out of Level 3	0	0	0	0
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	261	224	261	224	260	253	201	210
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	1	23	8	14
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Retained Interest [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	31	45	31	45	34	35	52	39
Net realized/unrealized gains (losses) included in earnings	0	1	0	(18)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(4)	(4)	(8)	30
Purchases	4	0	9	0
Sales	(2)	(2)	(3)	(3)
Settlements	(1)	(2)	(2)	(3)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	14	22	14	22	15	17	21	24
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(1)	1	(2)	0
Purchases	3	0	3	0
Sales	(4)	0	(4)	0
Settlements	1	0	0	0
Transfers into Level 3	0	0	0	1
Transfers out of Level 3	0	0	0	(3)
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	136	111	136	111	117	141	75	227
Net realized/unrealized gains (losses) included in earnings	21	37	(4)	55
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(2)	0	(1)	4
Purchases	20	1	20	5
Sales	(3)	0	(3)	0
Settlements	(13)	(2)	(13)	(186)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(4)	0	(4)	6
Net change in unrealized gains (losses) relating to instruments still held	30	12	1	32
Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	409	595	409	595	390	388	472	450
Net realized/unrealized gains (losses) included in earnings	2	3	4	3
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(13)	11	(13)	28
Purchases	34	114	34	119
Sales	(4)	0	(4)	0
Settlements	0	(5)	0	(5)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Net change in unrealized gains (losses) relating to instruments still held	(1)	1	1	1
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	10,119	9,297	10,119	9,297	9,959	9,519	8,746	8,670
Net realized/unrealized gains (losses) included in earnings	60	35	13	97
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(241)	50	(59)	204
Purchases	557	567	978	1,016
Sales	(130)	(86)	(264)	(342)
Settlements	(111)	(71)	(170)	(373)
Transfers into Level 3	126	169	224	256
Transfers out of Level 3	(101)	(113)	(122)	(231)
Net change in unrealized gains (losses) relating to instruments still held	$ 29	$ 13	$ 2	$ 33