Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Investments in Debt and Equity Securities
Cost Basis	$ 1,598	$ 1,577
Unrealized Pretax Net Gains (Losses)	72	58
Fair Value	1,670	1,635
U.S. treasury bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	12	9
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	12	9
Other U.S. and non-U.S. government bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	72	71
Unrealized Pretax Net Gains (Losses)	0	1
Fair Value	72	72
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	707	701
Unrealized Pretax Net Gains (Losses)	13	7
Fair Value	720	708
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	126	129
Unrealized Pretax Net Gains (Losses)	1	0
Fair Value	127	129
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	283	291
Unrealized Pretax Net Gains (Losses)	5	1
Fair Value	288	292
Residential
Schedule of Investments in Debt and Equity Securities
Cost Basis	11	12
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	11	12
Commercial
Schedule of Investments in Debt and Equity Securities
Cost Basis	58	59
Unrealized Pretax Net Gains (Losses)	2	2
Fair Value	60	61
Large capitalization value
Schedule of Investments in Debt and Equity Securities
Cost Basis	242	243
Unrealized Pretax Net Gains (Losses)	35	30
Fair Value	277	273
Real estate investment trust (REIT)
Schedule of Investments in Debt and Equity Securities
Cost Basis	50	25
Unrealized Pretax Net Gains (Losses)	1	0
Fair Value	51	25
Smaller company growth
Schedule of Investments in Debt and Equity Securities
Cost Basis	37	37
Unrealized Pretax Net Gains (Losses)	15	17
Fair Value	$ 52	$ 54