Investments-Fair Values (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 25,931	$ 27,427
Gross unrealized gains	2,318	1,747
Gross unrealized losses	(159)	(418)
Fair value	28,090	28,756
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	683	678
Gross unrealized gains	97	90
Gross unrealized losses	0	(2)
Fair value	780	766
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,129	3,135
Gross unrealized gains	432	231
Gross unrealized losses	(14)	(62)
Fair value	3,547	3,304
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19,550	20,397
Gross unrealized gains	1,579	1,214
Gross unrealized losses	(113)	(295)
Fair value	21,016	21,316
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	660	715
Gross unrealized gains	80	83
Gross unrealized losses	(1)	(6)
Fair value	739	792
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	723	1,011
Gross unrealized gains	18	30
Gross unrealized losses	(23)	(34)
Fair value	718	1,007
Residential mortgage-backed securities ("RMBS")
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	602	752
Gross unrealized gains	59	50
Gross unrealized losses	(5)	(12)
Fair value	656	790
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	570	724
Gross unrealized gains	50	47
Gross unrealized losses	(3)	(7)
Fair value	617	764
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	14	15
Gross unrealized gains	3	2
Gross unrealized losses	0	0
Fair value	$ 17	$ 17