Investments and Cash (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Investments
Percent of Total	100.00%	[1],[2]	100.00%	[1],[2]
Amortized Cost, total investment portfolio	$ 10,348	[1]	$ 10,163	[1]
Gross Unrealized Gains, total investment portfolio	424	[1]	808	[1]
Gross Unrealized Losses, total investment portfolio	(138)	[1]	(98)	[1]
Estimated Fair Value, total investment portfolio	10,634	[1]	10,873	[1]
AOCI Gain (Loss) on Securities with OTTI	(36)	[1],[3]	(7)	[1]
Percentage of mortgage backed securities representing government-agency obligations	51.00%		61.00%
Fixed maturity securities
Investments
Percent of Total	93.00%	[1],[2]	92.00%	[1],[2]
Available-for-sale Securities, Amortized Cost Basis	9,587	[1]	9,346	[1]
Gross Unrealized Gains, total fixed maturity securities	424	[1]	808	[1]
Gross Unrealized Losses, total fixed maturity securities	(138)	[1]	(98)	[1]
Estimated Fair Value, total fixed maturity securities	9,873	[1]	10,056	[1]
AOCI Gain (Loss) on Securities with OTTI	(36)	[1],[3]	(7)	[1]
U.S. government and agencies
Investments
Percent of Total	6.00%	[1],[2]	7.00%	[1],[2]
Available-for-sale Securities, Amortized Cost Basis	684	[1]	732	[1]
Gross Unrealized Gains, total fixed maturity securities	37	[1]	62	[1]
Gross Unrealized Losses, total fixed maturity securities	(4)	[1]	0	[1]
Estimated Fair Value, total fixed maturity securities	717	[1]	794	[1]
AOCI Gain (Loss) on Securities with OTTI	0	[1],[3]	0	[1]
Obligations of state and political subdivisions
Investments
Percent of Total	49.00%	[1],[2]	51.00%	[1],[2]
Available-for-sale Securities, Amortized Cost Basis	5,047	[1]	5,153	[1]
Gross Unrealized Gains, total fixed maturity securities	241	[1]	489	[1]
Gross Unrealized Losses, total fixed maturity securities	(39)	[1]	(11)	[1]
Estimated Fair Value, total fixed maturity securities	5,249	[1]	5,631	[1]
AOCI Gain (Loss) on Securities with OTTI	1	[1],[3]	9	[1]
Corporate securities
Investments
Percent of Total	13.00%	[1],[2]	9.00%	[1],[2]
Available-for-sale Securities, Amortized Cost Basis	1,308	[1]	930	[1]
Gross Unrealized Gains, total fixed maturity securities	50	[1]	80	[1]
Gross Unrealized Losses, total fixed maturity securities	(13)	[1]	0	[1]
Estimated Fair Value, total fixed maturity securities	1,345	[1]	1,010	[1]
AOCI Gain (Loss) on Securities with OTTI	0	[1],[3]	0	[1]
RMBS
Investments
Percent of Total	11.00%	[1],[2],[4]	13.00%	[1],[2],[4]
Available-for-sale Securities, Amortized Cost Basis	1,157	[1],[4]	1,281	[1],[4]
Gross Unrealized Gains, total fixed maturity securities	33	[1],[4]	62	[1],[4]
Gross Unrealized Losses, total fixed maturity securities	(70)	[1],[4]	(77)	[1],[4]
Estimated Fair Value, total fixed maturity securities	1,120	[1],[4]	1,266	[1],[4]
AOCI Gain (Loss) on Securities with OTTI	(53)	[1],[3],[4]	(59)	[1],[4]
CMBS
Investments
Percent of Total	5.00%	[1],[2],[4]	5.00%	[1],[2],[4]
Available-for-sale Securities, Amortized Cost Basis	507	[1],[4]	482	[1],[4]
Gross Unrealized Gains, total fixed maturity securities	19	[1],[4]	38	[1],[4]
Gross Unrealized Losses, total fixed maturity securities	(3)	[1],[4]	0	[1],[4]
Estimated Fair Value, total fixed maturity securities	523	[1],[4]	520	[1],[4]
AOCI Gain (Loss) on Securities with OTTI	0	[1],[3],[4]	0	[1],[4]
Asset-backed securities
Investments
Percent of Total	6.00%	[1],[2]	5.00%	[1],[2]
Available-for-sale Securities, Amortized Cost Basis	592	[1]	482	[1]
Gross Unrealized Gains, total fixed maturity securities	31	[1]	59	[1]
Gross Unrealized Losses, total fixed maturity securities	(9)	[1]	(10)	[1]
Estimated Fair Value, total fixed maturity securities	614	[1]	531	[1]
AOCI Gain (Loss) on Securities with OTTI	16	[1],[3]	43	[1]
Foreign government securities
Investments
Percent of Total	3.00%	[1],[2]	2.00%	[1],[2]
Available-for-sale Securities, Amortized Cost Basis	292	[1]	286	[1]
Gross Unrealized Gains, total fixed maturity securities	13	[1]	18	[1]
Gross Unrealized Losses, total fixed maturity securities	0	[1]	0	[1]
Estimated Fair Value, total fixed maturity securities	305	[1]	304	[1]
AOCI Gain (Loss) on Securities with OTTI	0	[1],[3]	0	[1]
Short-term investments
Investments
Percent of Total	7.00%	[1],[2]	8.00%	[1],[2]
Amortized Cost, total investment portfolio	761	[1]	817	[1]
Gross Unrealized Gains, total investment portfolio	0	[1]	0	[1]
Gross Unrealized Losses, total investment portfolio	0	[1]	0	[1]
Estimated Fair Value, total investment portfolio	761	[1]	817	[1]
AOCI Gain (Loss) on Securities with OTTI	$ 0	[1],[3]	$ 0	[1]

[1] Ratings in the tables above represent the lower of the Moody’s and S&P classifications except for bonds purchased for loss mitigation or risk management strategies, which use internal ratings classifications. The Company’s portfolio consists primarily of high-quality, liquid instruments.

[2] Based on amortized cost.

[3] Accumulated OCI ("AOCI").

[4] Government-agency obligations were approximately 51% of mortgage backed securities as of September 30, 2013 and 61% as of December 31, 2012 based on fair value.