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	$ 2,968		$ 2,816
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	3,104	3,571	2,953	3,591
Net realized/unrealized gains (losses) included in earnings	8	(271)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	60	219
Purchases	153	63
Sales	(2)	(6)
Settlements	(112)	(45)
Transfers into Level 3	97	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	1,072	1,349	1,064	1,218
Net realized/unrealized gains (losses) included in earnings	(21)	8
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	47	19
Purchases	219	825
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	158	343	164	416
Net realized/unrealized gains (losses) included in earnings	(7)	(19)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	0	(1)
Sales	0	0
Settlements	2	(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	0	12
Other 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	288	779	494	799
Net realized/unrealized gains (losses) included in earnings	3	(22)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	0	0
Purchases	83	57
Sales	(13)	(55)
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	(9)	(21)
Total [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Level 3	12,501	11,557	12,104	11,645
Net realized/unrealized gains (losses) included in earnings	(14)	(300)
Net realized/unrealized gains (losses) included in accumulated other comprehensive income	118	229
Purchases	870	1,092
Sales	(17)	(64)
Settlements	(729)	(1,100)
Transfers into Level 3	533	130
Transfers out of Level 3	(364)	(75)
Net change in unrealized gains (losses) relating to instruments still held	$ (9)	$ (9)