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	$ 3,097		$ 3,097
Domestic Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	3,372	3,097	3,372	3,097	3,252	3,235	3,120	3,199
Net realized/unrealized gains (losses) included in earnings	33	14	59	101
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(72)	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	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	348	297	348	297	321	369	272	265
Net realized/unrealized gains (losses) included in earnings	30	29	30	57
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(2)	0	(1)	4
Purchases	23	1	21	5
Sales	(3)	0	(3)	0
Settlements	(16)	(5)	(18)	(190)
Transfers into Level 3	(1)	0	(1)	150
Transfers out of Level 3	(4)	0	(49)	6
Net change in unrealized gains (losses) relating to instruments still held	39	4	32	35
Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	785	1,149	785	1,149	816	817	987	906
Net realized/unrealized gains (losses) included in earnings	27	43	32	102
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(13)	12	(13)	28
Purchases	40	112	41	118
Sales	(35)	0	(42)	0
Settlements	0	(5)	0	(5)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(50)	0	(50)	0
Net change in unrealized gains (losses) relating to instruments still held	29	39	34	96
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	10,707	10,038	10,707	10,038	10,590	10,176	9,459	9,165
Net realized/unrealized gains (losses) included in earnings	94	67	75	198
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(242)	51	(59)	204
Purchases	566	565	986	1,015
Sales	(161)	(86)	(302)	(342)
Settlements	(114)	(74)	(175)	(377)
Transfers into Level 3	125	169	223	406
Transfers out of Level 3	(151)	(113)	(217)	(231)
Net change in unrealized gains (losses) relating to instruments still held	$ 68	$ 43	$ 66	$ 131