Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	$ 2,855	$ 2,990	$ 2,855	$ 2,990
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	3,207	3,372	3,207	3,372	3,552	3,542	3,251	3,235
Net realized/unrealized gains (losses) included in earnings	7	33	(251)	59
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(4)	(71)	214	(34)
Purchases	33	119	94	132
Sales	(341)	(40)	(347)	(71)
Settlements	(45)	(31)	(90)	(47)
Transfers into Level 3	15	116	108	116
Transfers out of Level 3	0	(5)	(73)	(18)
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	91	97	91	97	100	96	107	41
Net realized/unrealized gains (losses) included in earnings	0	0	0	(3)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	1	0	(2)	3
Purchases	0	0	0	0
Sales	(2)	0	(2)	0
Settlements	(4)	(2)	(5)	(3)
Transfers into Level 3	0	1	0	69
Transfers out of Level 3	0	(9)	0	(10)
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	5	0	5	0	6	6	1	4
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	(1)	0	(1)
Settlements	(1)	0	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	(3)
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	98	81	98	81	77	90	79	77
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(4)	1	(4)	3
Purchases	12	1	16	1
Sales	0	0	0	0
Settlements	0	0	(1)	0
Transfers into Level 3	0	0	10	0
Transfers out of Level 3	0	0	0	0
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	1,184	1,363	1,184	1,363	1,212	1,336	1,249	1,204
Net realized/unrealized gains (losses) included in earnings	(91)	(3)	(83)	(12)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	7	(63)	20	(3)
Purchases	1	306	127	316
Sales	0	0	(3)	0
Settlements	(25)	(52)	(60)	(78)
Transfers into Level 3	0	9	15	23
Transfers out of Level 3	(44)	(83)	(44)	(87)
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	5,346	4,304	5,346	4,304	5,023	4,916	4,404	4,040
Net realized/unrealized gains (losses) included in earnings	1	7	2	3
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(66)	(89)	(68)	(47)
Purchases	766	57	910	398
Sales	(1)	(75)	(1)	(106)
Settlements	(263)	0	(525)	0
Transfers into Level 3	0	0	12	16
Transfers out of Level 3	(7)	0	(7)	0
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	38	51	38	51	42	41	52	84
Net realized/unrealized gains (losses) included in earnings	0	0	0	(34)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(3)	0	(4)	35
Purchases	0	13	0	65
Sales	0	(1)	0	(72)
Settlements	0	(13)	0	(27)
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
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	264	261	264	261	277	264	260	253
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	(13)	8
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	93	31	93	31	83	91	34	35
Net realized/unrealized gains (losses) included in earnings	2	0	5	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	6	(4)	16	(8)
Purchases	2	4	2	9
Sales	0	(2)	0	(3)
Settlements	(8)	(1)	(13)	(2)
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	14	11	14	13	11	15	17
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	3	0	3
Sales	0	(4)	0	(4)
Settlements	0	1	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	(2)	0
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	170	136	170	136	262	170	117	141
Net realized/unrealized gains (losses) included in earnings	(25)	21	(63)	(4)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	1	(2)	1	(1)
Purchases	(1)	20	(2)	20
Sales	0	(3)	0	(3)
Settlements	(1)	(13)	(54)	(13)
Transfers into Level 3	26	0	26	0
Transfers out of Level 3	0	(4)	0	(4)
Net change in unrealized gains (losses) relating to instruments still held	(27)	30	(34)	1
Other 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	438	409	438	409		409	390	388
Net realized/unrealized gains (losses) included in earnings	(100)	2	(102)	4
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	4	(13)	4	(13)	432
Purchases	126	34	159	34
Sales	(1)	(4)	(55)	(4)
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	(92)	(1)	(93)	1
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	10,945	10,119	10,945	10,119	11,079	10,972	9,959	9,519
Net realized/unrealized gains (losses) included in earnings	(206)	60	(492)	13
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(58)	(241)	164	(59)
Purchases	939	557	1,306	978
Sales	(345)	(130)	(408)	(264)
Settlements	(347)	(111)	(749)	(170)
Transfers into Level 3	41	126	171	224
Transfers out of Level 3	(51)	(101)	(126)	(122)
Net change in unrealized gains (losses) relating to instruments still held	$ (119)	$ 29	$ (127)	$ 2