Investments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available for Sale Securities
Amortized cost	$ 59,447	$ 59,008
Gross unrealized gains	3,356	2,475
Gross unrealized losses	(169)	(573)
Fair value	62,634	60,910
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost	4,707	2,791
Gross unrealized gains	147	129
Gross unrealized losses	(1)	(7)
Fair value	4,853	2,913
Municipal
Schedule of Available for Sale Securities
Amortized cost	8,009	8,446
Gross unrealized gains	572	364
Gross unrealized losses	(20)	(87)
Fair value	8,561	8,723
Corporate
Schedule of Available for Sale Securities
Amortized cost	39,282	39,331
Gross unrealized gains	2,283	1,659
Gross unrealized losses	(98)	(387)
Fair value	41,467	40,603
Foreign government
Schedule of Available for Sale Securities
Amortized cost	1,569	1,736
Gross unrealized gains	108	99
Gross unrealized losses	(1)	(11)
Fair value	1,676	1,824
Asset-backed securities ("ABS")
Schedule of Available for Sale Securities
Amortized cost	3,903	4,491
Gross unrealized gains	68	71
Gross unrealized losses	(28)	(44)
Fair value	3,943	4,518
Residential mortgage-backed securities ("RMBS")
Schedule of Available for Sale Securities
Amortized cost	1,263	1,403
Gross unrealized gains	117	101
Gross unrealized losses	(18)	(30)
Fair value	1,362	1,474
Commercial mortgage-backed securities ("CMBS")
Schedule of Available for Sale Securities
Amortized cost	692	788
Gross unrealized gains	57	48
Gross unrealized losses	(3)	(7)
Fair value	746	829
Redeemable preferred stock
Schedule of Available for Sale Securities
Amortized cost	22	22
Gross unrealized gains	4	4
Fair value	$ 26	$ 26