Investments in Debt and Equity Securities (Details 3) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 132
Due after one year through five years, Cost Basis	617
Due after five through ten years, Cost Basis	129
Due after ten years, Cost Basis	17
Due in one year or less, Fair Value	132
Due after one year through five years, Fair Value	618
Due after five years through ten years, Fair Value	129
Due after ten years, Fair Value	18
Cost Basis	1,224
Fair Value	1,225
Schedule of Investments in Debt and Equity Securities
Cost Basis	1,224		$ 1,171
Available-for-sale securities, fair value	1,225		1,151
Unrealized gain (loss) on equity securities	38	$ (2)
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	47	73
Gross gains from the sale of available-for-sale securities	0	0
Gross losses from the sale of available-for-sale securities	1	$ 0
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	305		301
Available-for-sale securities, fair value	304		297
Residential
Schedule of Investments in Debt and Equity Securities
Cost Basis	7		7
Available-for-sale securities, fair value	7		7
Commercial
Schedule of Investments in Debt and Equity Securities
Cost Basis	17		14
Available-for-sale securities, fair value	$ 17		$ 13