Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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%	14.80%	0.00%	6.40%
State income tax provisions, net of federal income tax benefit (in hundredths)	1.50%	3.50%	2.70%	3.80%
All other, net (in hundredths)	(1.70%)	(0.90%)	(1.00%)	(0.20%)
Effective tax rate (in hundredths)	34.80%	52.40%	36.70%	45.00%
Impact of charge resulting from increases in certain state tax laws		$ 10.5		$ 10.5
Amount of uncertain tax positions whose statute of limitations are expected to expire during the next twelve months	$ 14		$ 14