Stock-Based Compensation Plans - Nonqualified Stock Options (Details) - Nonqualified Stock Options - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in options outstanding
Options outstanding at beginning of period (in shares)	8.6
Options granted (in shares)	0.6
Options exercised (in shares)	1.3
Options expired (in shares)	0.2
Options outstanding at end of period (in shares)	7.7	8.6
Options vested or expected to vest at end of period (in shares)	7.7
Options exercisable at end of period (in shares)	6.5
Options outstanding at beginning of period weighted-average exercise price (in dollars per share)	$ 42.68
Options granted weighted-average exercise price (in dollars per share)	51.33
Options exercised weighted-average exercise price (in dollars per share)	40.00
Options expired weighted-average exercise price (in dollars per share)	48.21
Options outstanding at end of period weighted-average exercise price (in dollars per share)	43.71	$ 42.68
Options vested or expected to vest at end of period weighted-average exercise price (in dollars per share)	43.70
Options exercisable at end of period weighted-average exercise price (in dollars per share)	$ 43.47
Options outstanding at end of period intrinsic value	$ 63.4
Options vested or expected to vest at end of period intrinsic value	63.4
Options exercisable at end of period intrinsic value	59.7
Total intrinsic value of options exercised	$ 17.4	$ 25.4	$ 30.7
Assumptions used to estimate fair value of stock options granted during period
Weighted-average expected volatility (as a percent)	52.20%	53.20%	53.30%
Weighted-average expected term	6 years 6 months	6 years 6 months	6 years 6 months
Weighted-average risk-free interest rate (as a percent)	1.80%	2.00%	1.10%
Weighted-average expected dividend yield (as a percent)	2.81%	2.50%	3.00%
Weighted-average estimated fair value of stock options granted (in dollars per share)	$ 20.43	$ 18.89	$ 11.95
Other nonqualified stock option disclosures
Unrecognized compensation costs	$ 2.6
Weighted-average service period over which unrecognized compensation costs will be recognized	1 year 8 months 12 days
Cash received from stock options exercised	$ 52.7	$ 56.1	$ 105.6
Tax benefits realized for the tax deductions from options exercised	$ 6.0	$ 8.6	$ 10.6
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Weighted-average remaining contractual life for stock options exercisable	3 years 2 months 12 days
Range of exercise prices, Range 1
Change in options outstanding
Options outstanding at end of period (in shares)	0.8
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Lower limit of exercise price range (in dollars per share)	$ 11.07
Upper limit of exercise price range (in dollars per share)	$ 21.69
Weighted-average remaining contractual life	3 years 2 months 12 days
Range of exercise prices, Range 2
Change in options outstanding
Options outstanding at end of period (in shares)	1.8
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Lower limit of exercise price range (in dollars per share)	$ 21.70
Upper limit of exercise price range (in dollars per share)	$ 32.32
Weighted-average remaining contractual life	6 years
Range of exercise prices, Range 3
Change in options outstanding
Options outstanding at end of period (in shares)	0.4
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Lower limit of exercise price range (in dollars per share)	$ 32.33
Upper limit of exercise price range (in dollars per share)	$ 42.95
Weighted-average remaining contractual life	5 years 2 months 12 days
Range of exercise prices, Range 4
Change in options outstanding
Options outstanding at end of period (in shares)	1.8
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Lower limit of exercise price range (in dollars per share)	$ 42.96
Upper limit of exercise price range (in dollars per share)	$ 53.58
Weighted-average remaining contractual life	5 years 9 months 18 days
Range of exercise prices, Range 5
Change in options outstanding
Options outstanding at end of period (in shares)	2.9
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Lower limit of exercise price range (in dollars per share)	$ 53.59
Upper limit of exercise price range (in dollars per share)	$ 64.22
Weighted-average remaining contractual life	1 year 8 months 12 days
Range of exercise prices, Total Range
Change in options outstanding
Options outstanding at end of period (in shares)	7.7
Summary of weighted-average remaining contractual lives for stock options outstanding and range of exercise prices
Lower limit of exercise price range (in dollars per share)	$ 11.07
Upper limit of exercise price range (in dollars per share)	$ 64.22
Weighted-average remaining contractual life	4 years
2014 Stock Incentive Plan, Amended and Restated 2010 Stock Incentive Plan and Stock Incentive Plan
Stock-Based Compensation Plans - Disclosures
Option expiration period	10 years
Vesting period	3 years
Change in options outstanding
Options granted (in shares)	0.6	0.6	0.8