Employee Stock Compensation Plans - Stock Options (Details) - Stock Options [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning balance, Shares Under Option (in shares)	1,480
Vested, Shares Under Option (in shares)	(476)
Outstanding, Ending balance, Shares Under Option (in shares)	1,004	1,480
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, Beginning balance, Weighted Average Exercise Price per Share (in dollars per share)	$ 17.86
Vested, Weighted Average Exercise Price per Share (in dollars per share)	17.28
Outstanding, Ending balance, Weighted Average Exercise Price per Share (in dollars per share)	$ 18.14	$ 17.86
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Contratual Term (in years)	3 years 10 days
Outstanding, Aggregate Intrinsic Value	$ 6
Exercisable, Shares Under Option (in shares)	1,004
Exercisable, Weighted Average Exercise Price per Share (in dollars per share)	$ 18.14
Exercisable, Weighted Average Remaining Contractual Term (in years)	3 years 10 days
Exercisable, Aggregate Intrinsic Value	$ 6
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Fully vested and expected to vest, Shares Under Option (in shares)	1,004
Fully vested and expected to vest, Weighted Average Exercise Price per Share (in dollars per share)	$ 18.14
Fully vested and expected to vest, Weighted Average Remaining Contractual Term (in years)	3 years 10 days
Fully vested and expected to vest, Aggregate Intrinsic Value	$ 6
Total intrinsic value of all options exercised	6	$ 8	$ 37
Cash received from option exercises	8	7	51
Tax benefit realized from these exercises	$ 2	$ 2	$ 12
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vesting period	1 year
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vesting period	10 years