Earnings Per Common Share - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2014
Antidilutive securities excluded from computation of earnings per share
Remaining number of shares authorized to be repurchased (in shares)	21,800		21,800		50,000
Repurchase and retirement of common stock (in shares)			6,000
Total consideration for repurchase of common stock including unpaid cash			$ 174
Payments for repurchase of common stock			$ 168	$ 207
Dividends
Cash dividends per common share paid (in dollars per share)	$ 0.095	$ 0.090	$ 0.19	$ 0.18
Cash dividends per common share declared (in dollars per share)	$ 0.095	$ 0.090	$ 0.19	$ 0.18
Stock Options
Antidilutive securities excluded from computation of earnings per share
Antidilutive effect on computation of diluted earnings per common share (in shares)	380	6,000	1,000	9,000
Long-term stock awards
Antidilutive securities excluded from computation of earnings per share
Repurchase and retirement of common stock to offset the dilutive impact of stock awards (in shares)			1,100