Investments in Debt and Equity Securities (Details 3) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 198
Due after one year through five years, Cost Basis	386
Due after five through ten years, Cost Basis	24
Due after ten years, Cost Basis	26
Due in one year or less, Fair Value	200
Due after one year through five years, Fair Value	387
Due after five years through ten years, Fair Value	24
Due after ten years, Fair Value	26
Cost Basis	888
Fair Value	889
Schedule of Investments in Debt and Equity Securities
Cost Basis	1,294		$ 1,317
Available-for-sale securities, Fair Value	1,362		1,367
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	89	$ 49
Gross gains from the sale of available-for-sale securities	1	1
Gross losses from the sale of available-for-sale securities	1	$ 1
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	214		225
Available-for-sale securities, Fair Value	212		223
Residential
Schedule of Investments in Debt and Equity Securities
Cost Basis	9		10
Available-for-sale securities, Fair Value	9		10
Commercial
Schedule of Investments in Debt and Equity Securities
Cost Basis	31		36
Available-for-sale securities, Fair Value	$ 31		$ 36