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Business and Summary of Significant Accounting Policies - Revision of Prior Periods (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consolidated Statements of Income
Income taxes									$ 235.6	$ 263.4	$ 246.1
Net income									739.0	827.2	767.4
Net income (controlling interest)	$ 150.2	$ 110.2	$ 108.3	$ 104.0	$ 147.5	$ 107.7	$ 127.6	$ 126.7	$ 472.8	$ 509.5	$ 433.9
Earnings per share - basic (in dollars per share)									$ 8.73	$ 9.37	$ 7.89
Earnings per share - diluted (in dollars per share)	$ 2.67	$ 2.02	$ 1.98	$ 1.90	$ 2.67	$ 1.96	$ 2.29	$ 2.26	$ 8.57	$ 9.17	$ 7.70
Consolidated Balance Sheet
Additional paid-in capital	$ 1,073.5				$ 694.9				$ 1,073.5	$ 694.9
Retained earnings	$ 3,054.4				2,581.6				3,054.4	2,581.6
Consolidated Statements of Cash Flows
Net income									739.0	827.2	$ 767.4
Deferred income tax provision									$ 59.3	101.2	81.0
Adjustment for Deferred Tax Benefit | Scenario, Previously Reported
Consolidated Statements of Income
Income taxes										256.9	227.9
Net income										833.7	785.6
Net income (controlling interest)										$ 516.0	$ 452.1
Earnings per share - basic (in dollars per share)										$ 9.49	$ 8.22
Earnings per share - diluted (in dollars per share)										$ 9.28	$ 8.01
Consolidated Balance Sheet
Additional paid-in capital					597.2					$ 597.2
Retained earnings					2,679.3					2,679.3
Consolidated Statements of Cash Flows
Net income										833.7	$ 785.6
Deferred income tax provision										94.7	62.8
Adjustment for Deferred Tax Benefit | Restatement Adjustment
Consolidated Statements of Income
Income taxes										6.5	18.2
Net income										(6.5)	(18.2)
Net income (controlling interest)										$ (6.5)	$ (18.2)
Earnings per share - basic (in dollars per share)										$ (0.12)	$ (0.33)
Earnings per share - diluted (in dollars per share)										$ (0.11)	$ (0.31)
Consolidated Balance Sheet
Additional paid-in capital					97.7					$ 97.7
Retained earnings					$ (97.7)					(97.7)
Consolidated Statements of Cash Flows
Net income										(6.5)	$ (18.2)
Deferred income tax provision										$ 6.5	$ 18.2

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