Income Per Common Share - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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)			6,700,000
Remaining amount authorized to be repurchased	$ 1,000,000,000		$ 1,000,000,000
Dividends
Cash dividends per common share paid (in dollars per share)	$ 0.105	$ 0.1	$ 0.21	$ 0.2
Cash dividends per common share declared (in dollars per share)	$ 0.105	$ 0.100	$ 0.21	$ 0.200
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)	675,000	397,000	606,000	310,000
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