Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	$ 2,990
Domestic Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	3,552	3,235	3,198
Net realized/unrealized gains (losses) included in earnings	66	78
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	32	(157)
Purchases	444	235
Sales	(214)	(182)
Settlements	(110)	(112)
Transfers into Level 3	299	182
Transfers out of Level 3	(200)	(7)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	100	41	66
Net realized/unrealized gains (losses) included in earnings	(3)	(3)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	1	1
Purchases	6	2
Sales	0	(5)
Settlements	(3)	(1)
Transfers into Level 3	135	71
Transfers out of Level 3	(77)	(90)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	6	4	49
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(1)	0
Purchases	0	6
Sales	0	0
Settlements	0	(4)
Transfers into Level 3	6	3
Transfers out of Level 3	(3)	(50)
Net change in unrealized gains (losses) relating to instruments still held	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	77	77	225
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	10	0
Purchases	16	12
Sales	0	0
Settlements	(1)	(8)
Transfers into Level 3	78	0
Transfers out of Level 3	(103)	(152)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Foreign Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	1,212	1,204	1,486
Net realized/unrealized gains (losses) included in earnings	(11)	(47)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	19	(91)
Purchases	335	25
Sales	(51)	(55)
Settlements	(172)	(118)
Transfers into Level 3	24	85
Transfers out of Level 3	(136)	(81)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	5,023	4,040	2,540
Net realized/unrealized gains (losses) included in earnings	1	(10)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(25)	61
Purchases	1,490	2,157
Sales	(502)	(185)
Settlements	0	(11)
Transfers into Level 3	25	1
Transfers out of Level 3	(6)	(513)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Foreign Government Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	42	84	156
Net realized/unrealized gains (losses) included in earnings	(33)	(100)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	38	48
Purchases	65	41
Sales	(72)	(1)
Settlements	(40)	(27)
Transfers into Level 3	0	107
Transfers out of Level 3	0	(140)
Net change in unrealized gains (losses) relating to instruments still held	0	0
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	277	253	210
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	24	43
Purchases	0	500
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(500)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Retained Interest [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	83	35	39
Net realized/unrealized gains (losses) included in earnings	(1)	(28)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(3)	26
Purchases	16	8
Sales	(6)	(5)
Settlements	(12)	(5)
Transfers into Level 3	54	0
Transfers out of Level 3	0	0
Net change in unrealized gains (losses) relating to instruments still held	0	0
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	13	17	24
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(1)	0
Purchases	3	0
Sales	(3)	0
Settlements	(1)	0
Transfers into Level 3	2	4
Transfers out of Level 3	(4)	(11)
Net change in unrealized gains (losses) relating to instruments still held	0	0
Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	0	0	0
Net realized/unrealized gains (losses) 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	0
Net change in unrealized gains (losses) relating to instruments still held	0	0
Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	262	141	227
Net realized/unrealized gains (losses) included in earnings	(11)	102
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(1)	2
Purchases	(2)	2
Sales	0	0
Settlements	(39)	(198)
Transfers into Level 3	178	0
Transfers out of Level 3	(4)	6
Net change in unrealized gains (losses) relating to instruments still held	160	81
Other Items [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	432	388	450
Net realized/unrealized gains (losses) included in earnings	2	4
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	2	(9)
Purchases	152	149
Sales	(70)	(145)
Settlements	0	(6)
Transfers into Level 3	0	0
Transfers out of Level 3	(42)	(55)
Net change in unrealized gains (losses) relating to instruments still held	(1)	0
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	11,079	9,519	8,670
Net realized/unrealized gains (losses) included in earnings	10	(4)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	95	(76)
Purchases	2,525	3,137
Sales	(918)	(578)
Settlements	(378)	(490)
Transfers into Level 3	801	453
Transfers out of Level 3	(575)	(1,593)
Net change in unrealized gains (losses) relating to instruments still held	$ 159	$ 81