Fair Value Measurements (Changes in Level 3 Instruments) (Details) - Level 3 - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance			$ 2,596
Changes in Level 3, ending balance	$ 2,665		2,665
Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash Accruals Not Included In Schedule Assets Measured For Fair Value On Recurring Basis	11	$ 8	11	$ 8
Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	225
Net realized/unrealized gains (losses) included in earnings	4
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0
Purchases	0
Sales	(7)
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	0
Changes in Level 3, ending balance	222		222
Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	4,245	4,333	4,246	4,128
Net realized/unrealized gains (losses) included in earnings	(24)	40	(45)	52
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(163)	116	(75)	199
Purchases	93	207	188	372
Sales	(50)	(231)	(165)	(243)
Settlements	(34)	(32)	(82)	(87)
Transfers into Level 3	42	42	42	140
Transfers out of Level 3	(26)	(80)	(26)	(166)
Changes in Level 3, ending balance	4,083	4,395	4,083	4,395
Net change in unrealized gains (losses) relating to instruments still held	(6)	17	(40)	19
Recurring | Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	40	26	29	20
Net realized/unrealized gains (losses) included in earnings	(4)	4	(1)	7
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0	2	0
Purchases	0	(3)	1	1
Sales	0	0	0	0
Settlements	(6)	3	(8)	3
Transfers into Level 3	42	0	42	(1)
Transfers out of Level 3	0	(1)	0	(1)
Changes in Level 3, ending balance	72	29	72	29
Net change in unrealized gains (losses) relating to instruments still held	(7)	3	(3)	14
Recurring | Retained interest
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance		1	1	1
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
Changes in Level 3, ending balance		1		1
Net change in unrealized gains (losses) relating to instruments still held		0		0
Recurring | Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	225	189	217	201
Net realized/unrealized gains (losses) included in earnings	4	10	(34)	11
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0	0	0
Purchases	0	20	0	20
Sales	(7)	(2)	(21)	(15)
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Changes in Level 3, ending balance	222	217	222	217
Net change in unrealized gains (losses) relating to instruments still held	1	14	(37)	5
US Corporate | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	3,163	3,011	3,056	2,787
Net realized/unrealized gains (losses) included in earnings	(10)	12	(3)	18
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(145)	56	(86)	119
Purchases	87	187	181	339
Sales	(38)	(157)	(55)	(156)
Settlements	(20)	(27)	(56)	(68)
Transfers into Level 3	0	41	0	138
Transfers out of Level 3	(13)	(63)	(13)	(117)
Changes in Level 3, ending balance	3,024	3,060	3,024	3,060
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
State and municipal | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	114	105	115	96
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(5)	4	(4)	7
Purchases	0	1	0	10
Sales	0	0	0	0
Settlements	(8)	0	(10)	(3)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Changes in Level 3, ending balance	101	110	101	110
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Residential Mortgage Backed Securities | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	2	81	16	86
Net realized/unrealized gains (losses) included in earnings	0	1	5	1
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	1	(4)	0
Purchases	0	0	0	0
Sales	0	(16)	(15)	(16)
Settlements	0	(1)	0	(5)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Changes in Level 3, ending balance	2	66	2	66
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Commercial mortgage backed | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	2	12	9	10
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	0	(7)	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	2
Transfers out of Level 3	0	0	0	0
Changes in Level 3, ending balance	2	12	2	12
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Asset-backed | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	111	142	123	145
Net realized/unrealized gains (losses) included in earnings	(14)	1	(14)	2
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(8)	2	(5)	4
Purchases	0	0	0	0
Sales	0	0	(12)	0
Settlements	0	(5)	(3)	(11)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(13)	(10)	(13)	(10)
Changes in Level 3, ending balance	76	130	76	130
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Corporate - non-U.S. | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	290	522	337	515
Net realized/unrealized gains (losses) included in earnings	0	12	0	13
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(7)	36	(4)	43
Purchases	0	0	0	0
Sales	0	(54)	(50)	(54)
Settlements	0	0	0	(1)
Transfers into Level 3	0	1	0	1
Transfers out of Level 3	0	(6)	0	(6)
Changes in Level 3, ending balance	283	511	283	511
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Government - non-U.S. | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	2	1	2	31
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	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	(30)
Changes in Level 3, ending balance	2	1	2	1
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
U.S. Government and federal agency | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	291	232	266	225
Net realized/unrealized gains (losses) included in earnings	0	0	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	2	17	28	26
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	(2)
Changes in Level 3, ending balance	293	249	293	249
Net change in unrealized gains (losses) relating to instruments still held	0	0	0	0
Available-for-sale Securities | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3, beginning balance	5	11	9	11
Net realized/unrealized gains (losses) included in earnings	0	0	2	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0	(2)	0
Purchases	6	2	6	2
Sales	(5)	(2)	(5)	(2)
Settlements	0	(2)	(4)	(2)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Changes in Level 3, ending balance	6	9	6	9
Net change in unrealized gains (losses) relating to instruments still held	$ 0	$ 0	$ 0	$ 0