Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Common Stock	Retained earnings	AOCI	Non-controlling interests
Beginning balance (in shares) at Dec. 31, 2016		141,791,153
Beginning balance at Dec. 31, 2016	$ 3,833.2	$ 2,727.3	$ 1,078.6	$ 0.0	$ 27.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	336.5		323.9		12.6
Issuance of stock (in shares)		12,131
Issuance of stock	0.6	$ 0.6
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		290,991
Issuance of stock compensation and reinvested dividends, net of tax withholding	(1.9)	$ (1.9)
Dividends declared on common stock	(229.2)		(229.2)
Stock compensation expense	8.8	$ 8.8
Deconsolidation of noncontrolling interests	(81.9)				(81.9)
Distributions to shareholders of noncontrolling interests	(5.7)				(5.7)
Change in unrecognized pension expense, net of tax	0.0
Ending balance (in shares) at Dec. 31, 2017		142,094,275
Ending balance at Dec. 31, 2017	3,860.4	$ 2,734.8	1,173.3	0.0	(47.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	546.0		535.8		10.2
Issuance of stock (in shares)		128,947,518
Issuance of stock	6,979.9	$ 6,979.9
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		533,273
Issuance of stock compensation and reinvested dividends, net of tax withholding	(16.7)	$ (16.7)
Dividends declared on common stock	(362.1)		(362.1)
Stock compensation expense	29.9	$ 29.9
Issuance of restricted common stock (in shares)		122,505
Dividend equivalents declared	(1.0)		(1.0)
Repurchase of common stock (in shares)		(16,371,319)
Repurchase of common stock	(1,042.3)	$ (1,042.3)
Derivative hedging activity, net of tax	(4.0)			(4.0)
Change in unrecognized pension expense, net of tax	1.0			1.0
Other	(0.4)	$ (0.4)
Ending balance (in shares) at Dec. 31, 2018		255,326,252
Ending balance at Dec. 31, 2018	9,990.7	$ 8,685.2	1,346.0	(3.0)	(37.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	685.6		669.9		15.7
Issuance of stock compensation and reinvested dividends, net of tax withholding (in shares)		111,849
Issuance of stock compensation and reinvested dividends, net of tax withholding	(2.4)	$ (2.4)
Dividends declared on common stock	(462.5)		(462.5)
Stock compensation expense	16.3	$ 16.3
Deconsolidation of noncontrolling interests	3.8				3.8
Distributions to shareholders of noncontrolling interests	(8.6)				(8.6)
Dividend equivalents declared	(1.9)		(1.9)
Repurchase of common stock (in shares)		(28,796,658)
Repurchase of common stock	(1,628.7)	$ (1,628.7)
Derivative hedging activity, net of tax	(46.4)			(46.4)
Change in unrecognized pension expense, net of tax	(0.6)			(0.6)
Ending balance (in shares) at Dec. 31, 2019		226,641,443
Ending balance at Dec. 31, 2019	$ 8,545.3	$ 7,070.4	$ 1,551.5	$ (50.0)	$ (26.6)