Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Investments in Debt and Equity Securities
Cost basis	$ 1,304	$ 1,171
Unrealized pretax net gains (losses)	24	(20)
Fair Value	1,328	1,151
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	47	42
Unrealized pretax net gains (losses)	1	0
Fair Value	48	42
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	823	735
Unrealized pretax net gains (losses)	17	(15)
Fair Value	840	720
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost basis	53	63
Unrealized pretax net gains (losses)	0	0
Fair Value	53	63
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost basis	326	301
Unrealized pretax net gains (losses)	5	(4)
Fair Value	331	297
Residential
Schedule of Investments in Debt and Equity Securities
Cost basis	6	7
Unrealized pretax net gains (losses)	0	0
Fair Value	6	7
Commercial
Schedule of Investments in Debt and Equity Securities
Cost basis	40	14
Unrealized pretax net gains (losses)	1	(1)
Fair Value	$ 41	$ 13