Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended
	Mar. 31, 2012	Feb. 29, 2012	Mar. 31, 2012	Mar. 31, 2011
Dilutive Impact of Common Stock Equivalents on Earning per Share (Abstract]
Net income			$ 183,893	$ 203,569
Less: Dividend requirements on preferred stock			0	(1,060)
Basic earnings per share [Abstract]
Earnings available to common shareholders			183,893	202,509
Weighted average common shares outstanding - basic (in shares)			487,360,000	483,641,000
Earnings available to common shareholders - basic (in dollars per share)			$ 0.38	$ 0.42
Effect of dilutive securities [Abstract]
401(k) equity awards (in shares)			635,000	660,000
Diluted earnings per share [Abstract]
Earnings available to common shareholders			$ 183,893	$ 202,509
Weighted average common shares outstanding - diluted (in shares)			487,995,000	484,301,000
Earnings available to common shareholders - diluted (in dollars per share)			$ 0.38	$ 0.42
Antidilutive weighted-average options outstanding excluded from earnings per share calculation (in shares)			0	2,500,000
Shares Repurchase [Abstract]
Number of shares of common stock approved to be repurchased (in shares)		700,000
Number of shares of common stock repurchased (in shares)	700,000
Average purchase price per share of common stock repurchased (in dollars per share)	$ 26.42
Number of shares of common stock purchased for settlement of equity awards (in shares)		900,000