CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 188.3	$ 99.7
Cash flow hedges
Unrealized net gains (losses) arising during period, net of tax of $ - million and $(0.2) million, respectively	0.1	(0.3)
Reclassification of net losses to net income, net of tax of $0.6 million and $1.0 million, respectively	0.9	1.5
Cash flow hedges, net	1.0	1.2
Defined benefit pension plans
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, net of tax of $0.4 million and $0.3 million, respectively	0.6	0.3
Other comprehensive income, net of tax	1.6	1.5
Comprehensive income	189.9	101.2
Preferred stock dividends of subsidiary	(0.8)	(0.8)
Comprehensive income attributed to common shareholders	$ 189.1	$ 100.4