CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net income	$ 99.7	$ 123.5
Cash flow hedges
Unrealized net losses arising during period, net of tax of $(0.2) million and $(2.4) million, respectively	(0.3)	(4.1)
Reclassification of net losses to net income, net of tax of $1.0 million and $5.1 million, respectively	1.5	8.4
Cash flow hedges, net	1.2	4.3
Defined benefit pension plans
Amortization of pension and other postretirement costs included in net periodic benefit cost, net of tax of $0.3 million and $0.2 million, respectively	0.3	0.2
Other comprehensive income, net of tax	1.5	4.5
Comprehensive income	101.2	128.0
Less: preferred stock dividends of subsidiary	(0.8)	(0.8)
Comprehensive income attributed to common shareholders	$ 100.4	$ 127.2