Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Amortized Cost	$ 10,822	$ 10,564
Estimated Fair Value
Estimated Fair Value	11,168	10,823
Fixed Maturities [Member]
Amortized Cost
Due within one year	284
Due after one year through five years	1,798
Due after five years through 10 years	2,171
Due after 10 years	4,343
Amortized Cost	10,135	9,974
Estimated Fair Value
Due within one year	283
Due after one year through five years	1,828
Due after five years through 10 years	2,227
Due after 10 years	4,581
Estimated Fair Value	10,479	10,233
Fixed Maturities [Member] | RMBS [Member]
Amortized Cost
Amortized Cost	978	998
Estimated Fair Value
Estimated Fair Value	992	987
Fixed Maturities [Member] | CMBS [Member]
Amortized Cost
Amortized Cost	561	575
Estimated Fair Value
Estimated Fair Value	$ 568	$ 583