Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments in Debt and Equity Securities
Cost Basis	$ 1,342	$ 1,317
Unrealized Pretax Net Gains (Losses)	81	50
Fair Value	1,423	1,367
U.S. treasury bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	10	9
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	10	9
Other U.S. and non-U.S. government bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	46	60
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	46	60
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	520	489
Unrealized Pretax Net Gains (Losses)	3	3
Fair Value	523	492
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	82	90
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	82	90
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	233	225
Unrealized Pretax Net Gains (Losses)	(1)	(2)
Fair Value	232	223
Residential
Schedule of Investments in Debt and Equity Securities
Cost Basis	9	10
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	9	10
Commercial
Schedule of Investments in Debt and Equity Securities
Cost Basis	26	36
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	26	36
Large capitalization value
Schedule of Investments in Debt and Equity Securities
Cost Basis	282	280
Unrealized Pretax Net Gains (Losses)	55	32
Fair Value	337	312
Real estate investment trust (REIT)
Schedule of Investments in Debt and Equity Securities
Cost Basis	93	77
Unrealized Pretax Net Gains (Losses)	4	2
Fair Value	97	79
Smaller company growth
Schedule of Investments in Debt and Equity Securities
Cost Basis	41	41
Unrealized Pretax Net Gains (Losses)	20	15
Fair Value	$ 61	$ 56