Stock-Based Compensation Plans - Nonqualified Stock Options (Details) - Nonqualified Stock Options $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Change in options outstanding
Options granted (in shares) | shares	0.7
Assumptions used to estimate fair value of stock options granted during period
Weighted-average expected volatility (as a percent)	27.60%
Weighted-average expected term	7 years
Weighted-average risk-free interest rate (as a percent)	2.20%
Weighted-average expected dividend yield (as a percent)	2.87%
Weighted-average estimated fair value of stock options granted (in dollars per share) | $ / shares	$ 15.31
Other nonqualified stock option disclosures
Unrecognized compensation costs | $	$ 5.5
Weighted-average service period over which unrecognized compensation costs will be recognized	1 year 2 months 12 days