Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Amounts attributable to common stockholders:
Income from continuing operations	$ 99,623	$ 101,570	$ 238,961	$ 189,756
Income (loss) from discontinued operations	0	(635)	19,332	(2,517)
Net Income (Loss) Available to Common Stockholders, Basic	99,623	100,935	258,293	187,239
Preferred Stock Dividends, Income Statement Impact	(13)	(14)	26	29
Income attributable to common stockholders (numerator for basic EPS)	$ 99,610	$ 100,921	$ 258,267	$ 187,210
Denominator (in thousands):
Weighted average shares used in basic EPS	200,252	203,171	200,091	203,372
Effect of dilutive shares:
Incremental Common Shares Attributable to Conversion of Preferred Stock	2	2	2	2
Incremental Common Shares Attributable to Conversion of Preference Stock	398	453	399	454
Incremental Common Shares Attributable to Share-based Payment Arrangements	459	459	407	399
Weighted-average shares used in diluted EPS	201,111	204,085	200,899	204,227
Income from continuing operations	$ 0.50	$ 0.50	$ 1.19	$ 0.93
Income (loss) from discontinued operations	$ 0.00	$ 0.00	$ 0.10	$ (0.01)
Net income	$ 0.50	$ 0.50	$ 1.29	$ 0.92
Diluted earnings per share:
Income from continuing operations	$ 0.50	$ 0.50	$ 1.19	$ 0.93
Income (loss) from discontinued operations	$ 0.00	$ 0.00	$ 0.10	$ (0.01)
Net income	$ 0.50	$ 0.49	$ 1.29	$ 0.92
Anti-dilutive shares (in thousands):
Anti-dilutive shares not used in calculating diluted weighted-average shares	13,737	14,224	14,517	14,023