Income Per Common Share - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	May 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amount authorized for repurchase					$ 1,500,000,000
Stock repurchased during period (in shares)			9,000,000
Remaining amount authorized to be repurchased	$ 936,000,000		$ 936,000,000
Dividends
Cash dividends per common share paid (in dollars per share)	$ 0.105	$ 0.1	$ 0.315	$ 0.3
Cash dividends per common share declared (in dollars per share)	$ 0.12	$ 0.105	$ 0.33	$ 0.305
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive effect on computation of diluted earnings per common share (in shares)	667,586	397,000	626,734	339,000
Long-term stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock repurchased and retired during period to offset dilutive impact of awards granted (in shares)			600,000