Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Amortized Cost
Amortized Cost		$ 10,747	$ 10,671
Estimated Fair Value
Estimated Fair Value		11,280	11,023
Fixed Maturities [Member]
Amortized Cost
Due within one year		416
Due after one year through five years		1,928
Due after five years through 10 years		2,110
Due after 10 years		4,065
Amortized Cost		10,219	10,275
Estimated Fair Value
Due within one year		436
Due after one year through five years		1,974
Due after five years through 10 years		2,216
Due after 10 years		4,372
Estimated Fair Value		10,752	10,627
Fixed Maturities [Member] | RMBS [Member]
Amortized Cost
Amortized Cost		1,082	1,238	[1]
Estimated Fair Value
Estimated Fair Value	[1]	1,105	1,245
Fixed Maturities [Member] | CMBS [Member]
Amortized Cost
Amortized Cost		618	506	[1]
Estimated Fair Value
Estimated Fair Value	[1]	$ 649	$ 513

[1] Government-agency obligations were approximately 44% of mortgage backed securities as of September 30, 2016 and 54% as of December 31, 2015 based on fair value.