Investments and Cash - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income
Gross investment income									$ 433	$ 412	$ 401
Investment expenses									(10)	(9)	(8)
Net investment income	$ 112	$ 112	$ 98	$ 101	$ 102	$ 102	$ 96	$ 103	423	403	393
Fixed Maturities, Managed Externally [Member]
Net Investment Income
Gross investment income									335	324	322
Fixed Maturities, Managed Internally [Member]
Net Investment Income
Gross investment income									61	74	74
Other Invested Assets, Internally Managed [Member]
Net Investment Income
Gross investment income									$ 37	$ 14	$ 5