Fair Value Measurements (Changes in Level 3 Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	$ 2,935		$ 2,813
Cash Accruals Not Included In Schedule Assets Measured For Fair Value On Recurring Basis	10	4
Domestic Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	3,071	3,542	2,918	3,552
Net realized/unrealized gains (losses) included in earnings	8	(258)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	63	218
Purchases	153	61
Sales	(2)	(6)
Settlements	(112)	(45)
Transfers into Level 3	96	93
Transfers out of Level 3	(53)	(73)
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	560	90	96	77
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	27	0
Purchases	9	4
Sales	0	0
Settlements	(7)	(1)
Transfers into Level 3	435	10
Transfers out of Level 3	0	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	81	96	86	100
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(1)	(3)
Purchases	0	0
Sales	0	0
Settlements	(4)	(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
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	11	6	10	6
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	(1)	0
Transfers into Level 3	2	0
Transfers out of Level 3	0	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	6,908	4,916	6,898	5,023
Net realized/unrealized gains (losses) included in earnings	1	1
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	(27)	(2)
Purchases	405	144
Sales	0	0
Settlements	(369)	(262)
Transfers into Level 3	0	12
Transfers out of Level 3	0	0
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	1,060	1,336	1,052	1,212
Net realized/unrealized gains (losses) included in earnings	(21)	8
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	46	13
Purchases	220	824
Sales	(2)	(3)
Settlements	(235)	(733)
Transfers into Level 3	0	15
Transfers out of Level 3	0	0
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	1	41	31	42
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	(1)
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(30)	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	232	264	225	277
Net realized/unrealized gains (losses) included in earnings	0	0
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	9	(13)
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(2)	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	75	91	72	83
Net realized/unrealized gains (losses) included in earnings	2	3
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	3	10
Purchases	1	0
Sales	0	0
Settlements	(3)	(5)
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	11	11	11	13
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	(2)
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	149	170	163	262
Net realized/unrealized gains (losses) included in earnings	(11)	(38)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	(1)	(1)
Sales	0	0
Settlements	(1)	(53)
Transfers into Level 3	(1)	0
Transfers out of Level 3	0	0
Net change in unrealized gains (losses) relating to instruments still held	(4)	(7)
Other 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	99	409	293	432
Net realized/unrealized gains (losses) included in earnings	2	(2)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	83	33
Sales	0	(54)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(279)	0
Net change in unrealized gains (losses) relating to instruments still held	0	(1)
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	12,258	10,972	11,855	11,079
Net realized/unrealized gains (losses) included in earnings	(19)	(286)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	120	222
Purchases	870	1,065
Sales	(4)	(63)
Settlements	(732)	(1,100)
Transfers into Level 3	532	130
Transfers out of Level 3	(364)	(75)
Net change in unrealized gains (losses) relating to instruments still held	$ (4)	$ (8)