Recent Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Jan. 01, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (Benefit) for Income Taxes	$ 116.1			$ 118.6		$ 361.6	$ 380.1
Net Income	257.6			234.6		766.0	734.5
Earnings Allocated to Participating Securities	4.8			3.8		13.7	11.6
Net Income Applicable to Common Stock	$ 251.7			$ 228.8		$ 748.4	$ 717.0
Effective tax rate	31.10%			33.60%		32.10%	34.10%
Basic Net Income Per Common Share (in dollars per share)	$ 1.09			$ 0.97		$ 3.23	$ 3.03
Diluted Net Income Per Common Share (in dollars per share)	$ 1.08			$ 0.96		$ 3.21	$ 3.00
Diluted Weighted Average Shares Outstanding (in shares)	228,055,195			234,163,190		229,040,618	234,890,782
Additional Paid-In Capital	$ 1,038.6					$ 1,038.6			$ 1,072.3
Retained Earnings	8,736.1					$ 8,736.1			$ 8,242.8
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (Benefit) for Income Taxes	$ (6.4)				$ 5.9
Basic Net Income Per Common Share (in dollars per share)	$ 0.03
Diluted Net Income Per Common Share (in dollars per share)	$ 0.06
Additional Paid-In Capital								$ (5.9)
Adjustments for New Accounting Principle, Early Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (Benefit) for Income Taxes		$ 131.7	$ 113.8
Net Income		263.0	245.4
Earnings Allocated to Participating Securities		4.8	4.1
Net Income Applicable to Common Stock		$ 257.2	$ 239.5
Effective tax rate		33.40%	31.70%
Basic Net Income Per Common Share (in dollars per share)		$ 1.11	$ 1.03
Diluted Net Income Per Common Share (in dollars per share)		$ 1.10	$ 1.03
Diluted Weighted Average Shares Outstanding (in shares)		229,280,000	229,798,000
Additional Paid-In Capital		$ 1,037.9	$ 1,018.5		1,037.9
Retained Earnings		8,568.6	8,398.4		8,568.6
Adjustments for New Accounting Principle, Early Adoption | Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (Benefit) for Income Taxes		134.0	117.4
Net Income		260.7	241.8
Earnings Allocated to Participating Securities		4.7	4.1
Net Income Applicable to Common Stock		$ 254.9	$ 235.9
Effective tax rate		33.90%	32.70%
Basic Net Income Per Common Share (in dollars per share)		$ 1.10	$ 1.01
Diluted Net Income Per Common Share (in dollars per share)		$ 1.09	$ 1.01
Diluted Weighted Average Shares Outstanding (in shares)		229,197,000	229,980,000
Additional Paid-In Capital		$ 1,040.2	$ 1,022.1		1,040.2
Retained Earnings		$ 8,566.3	$ 8,394.8		$ 8,566.3