Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Dilutive Impact of Common Stock Equivalents on Earnings per Share (Abstract]
Net income	$ 236,570	$ 183,893
Basic earnings per share [Abstract]
Earnings available to common shareholders	236,570	183,893
Weighted average common shares outstanding - basic (in shares)	489,781	487,360
Earnings available to common shareholders - basic (in dollars per share)	$ 0.48	$ 0.38
Effect of dilutive securities [Abstract]
401(k) equity awards (in shares)	750	635
Diluted earnings per share [Abstract]
Earnings available to common shareholders	$ 236,570	$ 183,893
Weighted average common shares outstanding - diluted (in shares)	490,531	487,995
Earnings available to common shareholders - diluted (in dollars per share)	$ 0.48	$ 0.38

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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