Common Stock - Stock Options Status and Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Tax benefit from options exercised				$ 6	$ 3
Total fair value of shares vested				$ 4	$ 6
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance	1,336,579	1,454,003		1,454,003
Canceled		(20,427)
Forfeited			(7,531)
Exercised	(141,644)	(96,997)
Outstanding, Ending Balance	1,187,404	1,336,579		1,187,404		1,454,003
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, Beginning Balance	$ 32.03	$ 31.16		$ 31.16
Canceled		23.75
Forfeited			$ 47.36
Exercised	14.68	20.78
Outstanding, Ending Balance	$ 34.00	$ 32.03		$ 34.00		$ 31.16
Weighted Avg. Remaining Life in Years		4 years 3 months 17 days		4 years 2 months 12 days		4 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 31	$ 33		$ 33
Aggregate Intrinsic Value, Exercised	6	3
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 30	$ 31		$ 30		$ 33