Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments in Debt and Equity Securities
Cost basis	$ 1,446	$ 1,340
Unrealized pretax net gains (losses)	3	25
Fair Value	1,449	1,365
U.S. treasury bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	9	9
Unrealized pretax net gains (losses)	0	0
Fair Value	9	9
Other U.S. and non-U.S. government bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	46	54
Unrealized pretax net gains (losses)	1	0
Fair Value	47	54
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	880	836
Unrealized pretax net gains (losses)	(9)	20
Fair Value	871	856
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost basis	87	62
Unrealized pretax net gains (losses)	(1)	0
Fair Value	86	62
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost basis	365	327
Unrealized pretax net gains (losses)	13	4
Fair Value	378	331
Residential
Schedule of Investments in Debt and Equity Securities
Cost basis	6	6
Unrealized pretax net gains (losses)	(1)	0
Fair Value	5	6
Commercial
Schedule of Investments in Debt and Equity Securities
Cost basis	53	46
Unrealized pretax net gains (losses)	0	1
Fair Value	$ 53	$ 47