Equity (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Other comprehensive income and total comprehensive income
Consolidated net income	$ 160,027	$ 633,069	$ 320,598	$ 253,678	$ 233,307	$ 497,901	$ 320,283	$ 218,814	$ 1,367,372	[1]	$ 1,270,305	[1]	$ 1,251,050	[1]
Other comprehensive income
Cash flow hedges net unrealized loss									71,239		(11,685)		(2,887)
Pension and other postretirement liabilities									(223,090)		(8,527)		(35,707)
Net unrealized investment gain (loss)									21,254		57,523		82,929
Foreign currency translation									357		(338)		(457)
Total comprehensive income									1,237,132		1,307,278		1,294,928
Equity (Textual) [Abstract]
Common stock repurchases									(234,632)		(878,576)		(613,125)
Common stock dividend									$ 3.32		$ 3.24		$ 3.00
Net of tax benefit in cash flow hedges net unrealized loss									34,411		(7,088)		333
Net of tax expense (benefit) in foreign currency translation									$ 192		$ (182)		$ (246)

[1] Consolidated net income and preferred dividend requirements of subsidiaries for 2011, 2010 and 2009 include $13.3 million of preferred dividends on subsidiaries' preferred stock without sinking fund that is not presented as equity.