Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions		Series A Preferred stock	Series B Preferred stock	Common stock	Additional paid-in capital	Retained earnings (accumulated deficit)	Accumulated other comprehensive income (loss)	Treasury stock	Noncontrolling interest	Total
Balances at Dec. 31, 2014		$ 0.0	$ 0.1	$ 4.6	$ 9,945.5	$ 6,114.1	$ 50.4	$ (5,930.7)	$ 48.0	$ 10,232.0
Increase (decrease) in stockholders' equity
Common stock issued				0.1	76.0					76.1
Stock-based compensation and additional related tax benefits					90.6	(6.5)			0.1	84.2
Treasury stock acquired, common								(300.6)		(300.6)
Dividends to common stockholders						(441.0)				(441.0)
Dividends to preferred stockholders						(16.5)				(16.5)
Preferred stock redemption			(0.1)		(541.7)	(8.2)				(550.0)
Distributions to noncontrolling interest									(15.4)	(15.4)
Contributions from noncontrolling interest									7.7	7.7
Purchase of subsidiary shares from noncontrolling interest	[1]				(19.0)		(10.3)		12.8	(16.5)
Adjustments to redemption amount of redeemable noncontrolling interest					(6.6)					(6.6)
Net income (loss)	[1]					1,234.0			14.3	1,248.3
Other comprehensive income (loss)	[1]						(922.6)		(1.7)	(924.3)
Balances at Dec. 31, 2015		0.0	0.0	4.7	9,544.8	6,875.9	(882.5)	(6,231.3)	65.8	9,377.4
Increase (decrease) in stockholders' equity
Common stock issued					37.8					37.8
Stock-based compensation and additional related tax benefits					92.5	(7.1)			0.4	85.8
Treasury stock acquired, common								(277.3)		(277.3)
Dividends to common stockholders						(464.9)				(464.9)
Distributions to noncontrolling interest									(34.8)	(34.8)
Contributions from noncontrolling interest									5.5	5.5
Purchase of subsidiary shares from noncontrolling interest	[1]				15.1		(9.3)			5.8
Adjustments to redemption amount of redeemable noncontrolling interest					(4.2)					(4.2)
Net income (loss)	[1]					1,316.5			28.5	1,345.0
Other comprehensive income (loss)	[1]						216.6		1.1	217.7
Balances at Dec. 31, 2016		0.0	0.0	4.7	9,686.0	7,720.4	(675.2)	(6,508.6)	66.5	10,293.8
Increase (decrease) in stockholders' equity
Common stock issued					162.5					162.5
Stock-based compensation					90.2	(7.9)			0.4	82.7
Treasury stock acquired, common								(220.4)		(220.4)
Dividends to common stockholders						(540.0)				(540.0)
Distributions to noncontrolling interest									(8.4)	(8.4)
Contributions from noncontrolling interest									6.0	6.0
Purchase of subsidiary shares from noncontrolling interest	[1]				(7.6)				(1.3)	(8.9)
Adjustments to redemption amount of redeemable noncontrolling interest					(5.9)					(5.9)
Net income (loss)	[1]					2,310.4			7.1	2,317.5
Other comprehensive income (loss)	[1]						840.7		2.3	843.0
Balances at Dec. 31, 2017		$ 0.0	$ 0.0	$ 4.7	$ 9,925.2	$ 9,482.9	$ 165.5	$ (6,729.0)	$ 72.6	$ 12,921.9

[1] Excludes amounts attributable to redeemable noncontrolling interest. See Note 13, Stockholders’ Equity, for further details.