Investments in Debt and Equity Securities (Details 2) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	$ 33	$ 338
Less than 12 months - Unrealized losses	1	3
12 months or more - Fair Value	29	666
12 months or more - Unrealized losses	1	18
Total - Fair Value	62	1,004
Total - Unrealized losses	2	21
Corporate bonds
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value	33	280
Less than 12 months - Unrealized losses	1	3
12 months or more - Fair Value	29	391
12 months or more - Unrealized losses	1	11
Total - Fair Value	62	671
Total - Unrealized losses	$ 2	14
Asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value		6
Less than 12 months - Unrealized losses		0
12 months or more - Fair Value		38
12 months or more - Unrealized losses		1
Total - Fair Value		44
Total - Unrealized losses		1
U.S. governmental agency mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value		52
Less than 12 months - Unrealized losses		0
12 months or more - Fair Value		223
12 months or more - Unrealized losses		5
Total - Fair Value		275
Total - Unrealized losses		5
Commercial
Available-for-sale Securities, Continuous Unrealized Loss Position
Less than 12 months - Fair Value		0
Less than 12 months - Unrealized losses		0
12 months or more - Fair Value		14
12 months or more - Unrealized losses		1
Total - Fair Value		14
Total - Unrealized losses		$ 1