Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Schedule of Investments in Debt and Equity Securities
Cost Basis	$ 1,658	$ 1,577
Unrealized Pretax Net Gains (Losses)	52	58
Fair Value	1,710	1,635
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	67	71
Unrealized Pretax Net Gains (Losses)	1	1
Fair Value	68	72
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	697	701
Unrealized Pretax Net Gains (Losses)	13	7
Fair Value	710	708
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	134	129
Unrealized Pretax Net Gains (Losses)	1	0
Fair Value	135	129
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	282	291
Unrealized Pretax Net Gains (Losses)	4	1
Fair Value	286	292
Residential
Schedule of Investments in Debt and Equity Securities
Cost Basis	10	12
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	10	12
Commercial
Schedule of Investments in Debt and Equity Securities
Cost Basis	62	59
Unrealized Pretax Net Gains (Losses)	1	2
Fair Value	63	61
Large capitalization value
Schedule of Investments in Debt and Equity Securities
Cost Basis	279	243
Unrealized Pretax Net Gains (Losses)	20	30
Fair Value	299	273
Real estate investment trust (REIT)
Schedule of Investments in Debt and Equity Securities
Cost Basis	70	25
Unrealized Pretax Net Gains (Losses)	2	0
Fair Value	72	25
Smaller company growth
Schedule of Investments in Debt and Equity Securities
Cost Basis	47	37
Unrealized Pretax Net Gains (Losses)	10	17
Fair Value	$ 57	$ 54