Earnings Per Share (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of the components of basic and diluted shares in the EPS Calculation [Abstract]
Weighted-average basic common shares outstanding (in shares)	176,500,000	177,400,000	175,400,000
Potential number of shares issuable under the Company's LTSIP (in shares)	1,000,000	1,400,000	2,600,000
Average diluted common shares outstanding (in shares)	177,500,000	178,800,000	178,000,000
Dividend Reinvestment and Stock Purchase Plan (Reinvestment Plan) [Abstract]
Shares issued	0	4,400	162,157
Shares reserved for future issuance	20,531,255
Stock Options [Member]
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 share-based award (in years)	6 months
Restricted Shares [Member] | Minimum [Member]
Long-Term Stock Incentive Plan [Abstract]
Vesting period for share-based award (in years)	3 years
Restricted Shares [Member] | Maximum [Member]
Long-Term Stock Incentive Plan [Abstract]
Vesting period for share-based award (in years)	4 years
Performance Shares [Member]
Long-Term Stock Incentive Plan [Abstract]
Performance share performance period (in years)	3 years