Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Schedule of Investments in Debt and Equity Securities
Cost Basis	$ 1,671	$ 1,577
Unrealized Pretax Net Gains (Losses)	55	58
Fair Value	1,726	1,635
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	69	71
Unrealized Pretax Net Gains (Losses)	1	1
Fair Value	70	72
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	718	701
Unrealized Pretax Net Gains (Losses)	16	7
Fair Value	734	708
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	135	129
Unrealized Pretax Net Gains (Losses)	2	0
Fair Value	137	129
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	294	291
Unrealized Pretax Net Gains (Losses)	6	1
Fair Value	300	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	57	59
Unrealized Pretax Net Gains (Losses)	1	2
Fair Value	58	61
Large capitalization value
Schedule of Investments in Debt and Equity Securities
Cost Basis	270	243
Unrealized Pretax Net Gains (Losses)	18	30
Fair Value	288	273
Real estate investment trust (REIT)
Schedule of Investments in Debt and Equity Securities
Cost Basis	63	25
Unrealized Pretax Net Gains (Losses)	1	0
Fair Value	64	25
Smaller company growth
Schedule of Investments in Debt and Equity Securities
Cost Basis	45	37
Unrealized Pretax Net Gains (Losses)	10	17
Fair Value	$ 55	$ 54