Earnings Per Share (Details)	12 Months Ended
	Dec. 31, 2011 installments Years	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of the components of basic and diluted shares in the EPS Calculation [Abstract]
Weighted-average basic common shares outstanding (in shares)	177,400,000	175,400,000	174,100,000
Potential number of shares issuable under the Long-term Stock Incentive Plan (in shares)	1,400,000	2,600,000	2,200,000
Average diluted common shares outstanding (in shares)	178,800,000	178,000,000	176,300,000
Dividend Reinvestment and Stock Purchase Plan (Reinvestment Plan) [Abstract]
Shares issued	4,400	162,157	181,508
Shares reserved for future issuance	20,918,482
Long-Term Stock Incentive Plan [Abstract]
Stock option minimum term (in years)	5 years
Stock option maximum term (in years)	10 years
Stock option majority minimum term (in years)	7 years
Stock option majority maximum term (in years)	10 years
Minimum number of installments for vesting of options held by employees	3
Maximum number of installments for vesting of options held by employees	4
Number of installments for vesting of options held by non-employee directors	1
Vesting period for options held by non-employee directors after grant (in months)	6 months
Minimum vesting period for majority of restricted shares (in years)	3 years
Maximum vesting period for majority of restricted shares (in years)	4 years
Performance share performance period (in years)	3
The date the share based award will be distributed	first quarter of 2014
End date of performance share performance period	12/31/2013