Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Condensed Financial Statements, Captions [Line Items]
Net Income	$ 70.4	$ 65.1	$ 171.8	$ 157.7
Other comprehensive income (loss):
Gain (loss) on cash flow hedges	7.0	(7.2)	2.5	(6.6)
Reclassification adjustment transferred to Net Income from cash flow hedges	1.0	0.1	1.1	0.5
Pension and other postretirement benefit costs	(1.9)	(1.8)	(3.6)	(3.5)
Total Comprehensive Income	76.5	56.2	171.8	148.1
Comprehensive loss attributable to noncontrolling interests	(0.1)	0	(0.1)	0
Comprehensive income attributable to controlling interests	76.6	56.2	171.9	148.1
Parent Guarantor [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income	70.5	65.1	171.9	157.7
Other comprehensive income (loss):
Gain (loss) on cash flow hedges	7.0	(7.2)	2.5	(6.6)
Reclassification adjustment transferred to Net Income from cash flow hedges	1.0	0.1	1.1	0.5
Pension and other postretirement benefit costs	(1.9)	(1.8)	(3.6)	(3.5)
Total Comprehensive Income	76.6	56.2	171.9	148.1
Comprehensive loss attributable to noncontrolling interests	0		0
Comprehensive income attributable to controlling interests	76.6		171.9
Subsidiary Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income	62.4	56.5	155.4	139.9
Other comprehensive income (loss):
Gain (loss) on cash flow hedges	7.0	(7.2)	2.5	(6.6)
Reclassification adjustment transferred to Net Income from cash flow hedges	0.4	0.4	0.9	0.8
Pension and other postretirement benefit costs	(1.9)	(1.8)	(3.6)	(3.5)
Total Comprehensive Income	67.9	47.9	155.2	130.6
Comprehensive loss attributable to noncontrolling interests	0		0
Comprehensive income attributable to controlling interests	67.9		155.2
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income	91.7	86.1	212.2	199.0
Other comprehensive income (loss):
Gain (loss) on cash flow hedges	7.0	(7.2)	2.5	(6.6)
Reclassification adjustment transferred to Net Income from cash flow hedges	0.6	(0.3)	0.2	(0.3)
Pension and other postretirement benefit costs	(1.9)	(1.8)	(3.6)	(3.5)
Total Comprehensive Income	97.4	76.8	211.3	188.6
Comprehensive loss attributable to noncontrolling interests	(0.1)		(0.1)
Comprehensive income attributable to controlling interests	97.5		211.4
Consolidation, Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income	(154.2)	(142.6)	(367.7)	(338.9)
Other comprehensive income (loss):
Gain (loss) on cash flow hedges	(14.0)	14.4	(5.0)	13.2
Reclassification adjustment transferred to Net Income from cash flow hedges	(1.0)	(0.1)	(1.1)	(0.5)
Pension and other postretirement benefit costs	3.8	3.6	7.2	7.0
Total Comprehensive Income	(165.4)	(124.7)	(366.6)	(319.2)
Comprehensive loss attributable to noncontrolling interests	0		0
Comprehensive income attributable to controlling interests	$ (165.4)		$ (366.6)