Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
Amortized Cost		$ 9,986	$ 10,671
Estimated Fair Value
Estimated Fair Value		10,545	11,023
Fixed Maturities [Member]
Amortized Cost
Due within one year		482
Due after one year through five years		1,484
Due after five years through 10 years		1,926
Due after 10 years		3,967
Amortized Cost		9,401	10,275
Estimated Fair Value
Due within one year		484
Due after one year through five years		1,536
Due after five years through 10 years		2,066
Due after 10 years		4,273
Estimated Fair Value		9,960	10,627
Fixed Maturities [Member] | RMBS [Member]
Amortized Cost
Amortized Cost		1,037	1,238	[1]
Estimated Fair Value
Estimated Fair Value	[1]	1,062	1,245
Fixed Maturities [Member] | CMBS [Member]
Amortized Cost
Amortized Cost		505	506	[1]
Estimated Fair Value
Estimated Fair Value	[1]	$ 539	$ 513

[1] Government-agency obligations were approximately 47% of mortgage backed securities as of June 30, 2016 and 54% as of December 31, 2015 based on fair value.