Statements of Condensed Consolidated Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income	Noncontrolling Interests in Consolidated Subsidiaries
Balance at Dec. 31, 2011	$ 3,593,830	$ 1,261,779	$ 2,143,910	$ 188,141
Balance (in shares) at Dec. 31, 2011		149,477
Increase (Decrease) in Stockholders' Equity
Net income	72,035		72,035
Other comprehensive income (loss)	62,887			62,887
Dividends on common stock ($0.03 and $0.22 per share for periods ending March 31, 2013 and 2012, respectively)	(32,938)		(32,938)
Stock-based compensation plans, net	10,320	10,320
Stock-based compensation plans, net (in shares)		98
Balance at Mar. 31, 2012	3,706,134	1,272,099	2,183,007	251,028
Balance (in shares) at Mar. 31, 2012		149,575
Balance at Dec. 31, 2012	3,888,802	1,308,771	2,195,502	99,547	284,982
Balance (in shares) at Dec. 31, 2012		150,109
Increase (Decrease) in Stockholders' Equity
Net income	109,281		100,255		9,026
Other comprehensive income (loss)	(77,965)			(77,965)
Dividends on common stock ($0.03 and $0.22 per share for periods ending March 31, 2013 and 2012, respectively)	(4,516)		(4,516)
Stock-based compensation plans, net	16,465	16,323			142
Stock-based compensation plans, net (in shares)		326
Distributions to noncontrolling interests ($0.35 per common unit)	(5,031)				(5,031)
Balance at Mar. 31, 2013	$ 3,927,036	$ 1,325,094	$ 2,291,241	$ 21,582	$ 289,119
Balance (in shares) at Mar. 31, 2013		150,435