Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Reconciliation of provision for income taxes computed at federal statutory rates to the effective rates [Abstract]
Consolidated tax provision at federal statutory rate (in hundredths)	35.00%	35.00%	35.00%	35.00%
Reversal of tax credits (in hundredths)	0.00%	0.00%	0.00%	5.90%
State income tax provisions, net of federal income tax benefit (in hundredths)	4.50%	9.60%	3.70%	3.80%
Tax reserve adjustment (in hundredths)	(7.10%)	(91.20%)	(4.00%)	(8.10%)
All other, net (in hundredths)	0.90%	1.40%	0.10%	0.70%
Effective tax rate (in hundredths)	33.30%	(45.20%)	34.80%	37.30%
Reversal of uncertain tax positions			$ 7.8	$ 14.0
Impact of charge resulting from increases in certain state tax laws			10.5
Amount of uncertain tax positions whose statute of limitations are expected to expire during the next twelve months	$ 6.3		$ 6.3