Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	$ 2,999
Domestic Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	3,252	3,120	3,235	3,199
Net realized/unrealized gains (losses) included in earnings	26	87
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	38	(23)
Purchases	13	45
Sales	(31)	(114)
Settlements	(16)	(74)
Transfers into Level 3	0	0
Transfers out of Level 3	(13)	0
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	107	118	41	66
Net realized/unrealized gains (losses) included in earnings	(3)	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	3	3
Purchases	0	1
Sales	0	(4)
Settlements	(1)	(1)
Transfers into Level 3	68	71
Transfers out of Level 3	(1)	(18)
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	1	11	4	49
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	7
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	3
Transfers out of Level 3	(3)	(48)
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	79	210	77	225
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	2	(5)
Purchases	0	4
Sales	0	0
Settlements	0	(3)
Transfers into Level 3	0	0
Transfers out of Level 3	0	(11)
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	1,249	1,479	1,204	1,486
Net realized/unrealized gains (losses) included in earnings	(9)	(27)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	60	54
Purchases	10	12
Sales	0	(28)
Settlements	(26)	(29)
Transfers into Level 3	14	11
Transfers out of Level 3	(4)	0
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	4,404	2,826	4,040	2,540
Net realized/unrealized gains (losses) included in earnings	(4)	3
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	42	74
Purchases	341	371
Sales	(31)	(109)
Settlements	0	(10)
Transfers into Level 3	16	1
Transfers out of Level 3	0	(44)
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	52	162	84	156
Net realized/unrealized gains (losses) included in earnings	(34)	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	35	6
Purchases	52	0
Sales	(71)	0
Settlements	(14)	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
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	260	201	253	210
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	7	(9)
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
Retained Interest [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	34	52	35	39
Net realized/unrealized gains (losses) included in earnings	0	(19)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(4)	34
Purchases	5	0
Sales	(1)	(1)
Settlements	(1)	(1)
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
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	15	21	17	24
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(1)	(1)
Purchases	0	0
Sales	0	0
Settlements	(1)	0
Transfers into Level 3	0	1
Transfers out of Level 3	0	(3)
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	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	321	272	369	265
Net realized/unrealized gains (losses) included in earnings	0	28
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	1	4
Purchases	(2)	4
Sales	0	0
Settlements	(2)	(185)
Transfers into Level 3	0	150
Transfers out of Level 3	(45)	6
Net change in unrealized gains (losses) relating to instruments still held	(3)	33
Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	816	987	817	906
Net realized/unrealized gains (losses) included in earnings	5	59
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	16
Purchases	1	6
Sales	(7)	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	5	57
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	10,590	9,459	10,176	9,165
Net realized/unrealized gains (losses) included in earnings	(19)	131
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	183	153
Purchases	420	450
Sales	(141)	(256)
Settlements	(61)	(303)
Transfers into Level 3	98	237
Transfers out of Level 3	(66)	(118)
Net change in unrealized gains (losses) relating to instruments still held	$ 2	$ 90