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, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based compensation, effect on earnings per share, basic (in dollars per share)	$ 0		$ 0	$ 0.01	$ 10,000
Shares Under Option
Outstanding, Beginning Balance (in shares)	1,125,527	1,144,719		1,144,719
Adjustment (in shares)		0
Forfeited (in shares)	(788)
Exercised (in shares)	(183,774)	(19,192)
Outstanding, Ending Balance (in shares)	940,965	1,125,527		940,965		1,144,719
Weighted Avg. Exercise Prices
Outstanding, Beginning Balance (in dollars per share)	$ 35.12	$ 34.69		$ 34.69
Adjustment (in dollars per share)		0.00
Forfeited (in dollars per share)	51.88
Exercised (in dollars per share)	23.07	9.31
Outstanding, Ending Balance (in dollars per share)	$ 37.46	$ 35.12		$ 37.46		$ 34.69
Weighted Avg. Remaining Life in Years		3 years 6 months		3 years 1 month 6 days		3 years 8 months
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 12	$ 19		$ 19
Aggregate Intrinsic Value, Exercised		1		5
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 14	$ 12		$ 14		$ 19
Share-based Compensation, Effect on Earnings Per Share, Diluted	$ 0		$ 0	$ 0.02