CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Premium on Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock [Member]
Changes in Stockholders' Equity
Balance	$ 4,005.1	$ 2.0	$ 1,125.7	$ 2,906.3	$ (28.9)	$ 0.0
Common Stock, Shares, Outstanding		199,700
Treasury Stock, Common, Shares						0
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0				0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	47.1	$ 0.0	0.0	47.1	0.0	$ 0.0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0				0
Dividends, Common Stock, Cash, Number of Shares		0				0
Other comprehensive income, net of tax	6.8	$ 0.0	0.0	0.0	6.8	$ 0.0
Dividends declared on common stock ($0.3875 per share)	(75.6)	$ 0.0	0.0	(75.6)	0.0	$ 0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		500				0
Stock-based compensation	(7.2)	$ 0.0	(7.2)	0.0	0.0	$ 0.0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	398.2			398.2
Other comprehensive income, net of tax	8.5
Treasury Stock, Value, Acquired, Cost Method	0.0
Balance	3,976.2	$ 2.0	1,118.5	2,877.8	(22.1)	$ 0.0
Common Stock, Shares, Outstanding		200,200
Treasury Stock, Common, Shares						0
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0				0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	100.2	$ 0.0	0.0	100.2	0.0	$ 0.0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0				0
Dividends, Common Stock, Cash, Number of Shares		0				0
Other comprehensive income, net of tax	1.0	$ 0.0	0.0	0.0	1.0	$ 0.0
Dividends declared on common stock ($0.3875 per share)	(73.1)	$ 0.0	0.0	(73.1)	0.0	$ 0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0				0
Stock-based compensation	2.9	$ 0.0	2.9	0.0	0.0	$ 0.0
Balance	4,007.2	$ 2.0	1,121.4	2,904.9	(21.1)	$ 0.0
Common Stock, Shares, Outstanding		200,200
Treasury Stock, Common, Shares						0
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0				0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	250.9	$ 0.0	0.0	250.9	0.0	$ 0.0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0				0
Dividends, Common Stock, Cash, Number of Shares		0				0
Other comprehensive income, net of tax	0.7	$ 0.0	0.0	0.0	0.7	$ 0.0
Dividends declared on common stock ($0.3875 per share)	(77.5)	$ 0.0	0.0	(77.5)	0.0	$ 0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0				0
Stock-based compensation	4.9	$ 0.0	4.9	0.0	0.0	$ 0.0
Balance	4,186.2	$ 2.0	1,126.3	3,078.3	(20.4)	$ 0.0
Common Stock, Shares, Outstanding		200,200
Treasury Stock, Common, Shares						0
Balance	4,139.5	$ 2.0	1,129.3	3,036.1	(27.9)	$ 0.0
Common Stock, Shares, Outstanding		200,100
Treasury Stock, Common, Shares						0
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0				0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(491.8)	$ 0.0	0.0	(491.8)	0.0	$ 0.0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0				0
Dividends, Common Stock, Cash, Number of Shares		0				0
Other comprehensive income, net of tax	(0.9)	$ 0.0	0.0	0.0	(0.9)	$ 0.0
Dividends declared on common stock ($0.3875 per share)	(79.3)	$ 0.0	0.0	(79.3)	0.0	$ 0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0				(200)
Stock-based compensation	(5.1)	$ 0.0	(14.5)	0.0	0.0	$ 9.4
Treasury Stock, Shares, Acquired		0				200
Treasury Stock, Value, Acquired, Cost Method	(9.7)	$ 0.0	0.0	0.0	0.0	$ (9.7)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(228.5)			(228.5)
Other comprehensive income, net of tax	$ 2.2
Treasury Stock, Shares, Acquired	405
Treasury Stock, Value, Acquired, Cost Method	$ 14.7
Balance	3,552.7	$ 2.0	1,114.8	2,465.0	(28.8)	$ (0.3)
Common Stock, Shares, Outstanding		200,100
Treasury Stock, Common, Shares						0
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0				0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	85.9	$ 0.0	0.0	85.9	0.0	$ 0.0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0				0
Dividends, Common Stock, Cash, Number of Shares		0				0
Other comprehensive income, net of tax	0.9	$ 0.0	0.0	0.0	0.9	$ 0.0
Dividends declared on common stock ($0.3875 per share)	(77.6)	$ 0.0	0.0	(77.6)	0.0	$ 0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0				0
Stock-based compensation	2.3	$ 0.0	2.3	0.0	0.0	$ 0.0
Balance	3,564.2	$ 2.0	1,117.1	2,473.3	(27.9)	$ (0.3)
Common Stock, Shares, Outstanding		200,100
Treasury Stock, Common, Shares						0
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0				0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	177.4	$ 0.0	0.0	177.4	0.0	$ 0.0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0				0
Dividends, Common Stock, Cash, Number of Shares		0				0
Other comprehensive income, net of tax	2.2	$ 0.0	0.0	0.0	2.2	$ 0.0
Dividends declared on common stock ($0.3875 per share)	(80.5)	$ 0.0	0.0	(80.5)	0.0	$ 0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0				0
Stock-based compensation	$ 2.4	$ 0.0	2.4	0.0	0.0	$ 0.0
Treasury Stock, Shares, Acquired	150	0				100
Treasury Stock, Value, Acquired, Cost Method	$ (5.0)	$ 0.0	0.0	0.0	0.0	$ (5.0)
Balance	$ 3,660.7	$ 2.0	$ 1,119.5	$ 2,570.2	$ (25.7)	$ (5.3)
Common Stock, Shares, Outstanding		200,100
Treasury Stock, Common, Shares						100