Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	$ 2,900		$ 2,900
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	3,578	3,667	3,578	3,667	3,235	3,372	3,096	3,198
Net realized/unrealized gains (losses) included in earnings	10	(22)	69	79
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	32	(32)	(2)	(52)
Purchases	70	530	202	605
Sales	(34)	(25)	(105)	(180)
Settlements	(16)	2	(63)	(101)
Transfers into Level 3	144	120	260	120
Transfers out of Level 3	0	(2)	(18)	(2)
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	34	44	34	44	41	97	45	66
Net realized/unrealized gains (losses) included in earnings	0	0	(3)	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(2)	(1)	1	0
Purchases	1	0	1	2
Sales	0	0	0	(4)
Settlements	0	0	(3)	(1)
Transfers into Level 3	5	0	74	71
Transfers out of Level 3	(67)	0	(77)	(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	6	8	6	8	4	0	7	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	2
Purchases	0	0	0	6
Sales	0	0	(1)	0
Settlements	0	0	0	0
Transfers into Level 3	6	0	6	3
Transfers out of Level 3	0	0	(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	153	89	153	89	77	81	209	225
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	8	4	11	(1)
Purchases	12	0	13	4
Sales	0	0	0	0
Settlements	(1)	(4)	(1)	(8)
Transfers into Level 3	78	0	78	0
Transfers out of Level 3	(25)	(120)	(25)	(131)
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	1,295	1,439	1,295	1,439	1,204	1,363	1,537	1,486
Net realized/unrealized gains (losses) included in earnings	(7)	1	(19)	(27)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	20	(55)	17	27
Purchases	18	0	334	12
Sales	(30)	(26)	(30)	(54)
Settlements	(59)	(14)	(137)	(74)
Transfers into Level 3	0	0	23	73
Transfers out of Level 3	(10)	(4)	(97)	(4)
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	4,819	2,905	4,819	2,905	4,040	4,304	3,132	2,540
Net realized/unrealized gains (losses) included in earnings	(3)	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	90	(65)	43	(10)
Purchases	483	269	881	1,049
Sales	(58)	(14)	(164)	(166)
Settlements	5	0	5	(11)
Transfers into Level 3	4	0	20	1
Transfers out of Level 3	(6)	(417)	(6)	(498)
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	41	112	41	112	84	51	274	156
Net realized/unrealized gains (losses) included in earnings	0	(1)	(34)	(17)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	2	(22)	37	(8)
Purchases	0	14	65	27
Sales	0	0	(72)	0
Settlements	(12)	(13)	(39)	(13)
Transfers into Level 3	0	0	0	107
Transfers out of Level 3	0	(140)	0	(140)
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	267	256	267	256	253	261	224	210
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	6	32	14	46
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	29	37	29	37	35	31	45	39
Net realized/unrealized gains (losses) included in earnings	1	(1)	1	(19)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	(6)	(8)	24
Purchases	3	1	12	1
Sales	(3)	(1)	(6)	(4)
Settlements	(3)	(1)	(5)	(4)
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	11	24	11	24	17	14	22	24
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)	(2)	(1)
Purchases	0	0	3	0
Sales	0	0	(4)	0
Settlements	(1)	0	(1)	0
Transfers into Level 3	1	3	1	4
Transfers out of Level 3	(3)	0	(3)	(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	145	134	145	134	141	136	111	227
Net realized/unrealized gains (losses) included in earnings	15	31	11	86
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0	(1)	4
Purchases	(8)	(3)	12	2
Sales	3	0	0	0
Settlements	(1)	(5)	(14)	(191)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	(4)	6
Net change in unrealized gains (losses) relating to instruments still held	9	35	9	67
Other 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	416	509	416	509		409	595	450
Net realized/unrealized gains (losses) included in earnings	(1)	(1)	3	2
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	9	(14)	(4)	14	388
Purchases	54	25	88	144
Sales	(55)	(95)	(59)	(95)
Settlements	0	(1)	0	(6)
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	0
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	10,794	9,224	10,794	9,224	9,519	10,119	9,297	8,670
Net realized/unrealized gains (losses) included in earnings	15	7	28	104
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	165	(159)	106	45
Purchases	633	836	1,611	1,852
Sales	(177)	(161)	(441)	(503)
Settlements	(88)	(36)	(258)	(409)
Transfers into Level 3	238	123	462	379
Transfers out of Level 3	(111)	(683)	(233)	(914)
Net change in unrealized gains (losses) relating to instruments still held	$ 8	$ 34	$ 10	$ 67