Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Sep. 30, 2010	Mar. 31, 2009 Fixed-Rate Notes [Member]	Dec. 31, 2010 ESOP debentures, 6.55% [Member]
Notes Payable	$ 6,387,400,000	$ 6,387,400,000			$ 2,400,000,000
Other Notes Payable	37,600,000	97,200,000				63,700,000
Long-term Debt, Fair Value Adjustment	556,500,000	304,100,000
Long-term Debt, Total	6,981,500,000	6,788,700,000
Long-term Debt, Current Maturities	(1,516,800,000)	(18,200,000)
Long-term debt	5,464,700,000	6,770,500,000
Short-term Bank Loans and Notes Payable	5,500,000	137,800,000		125,000,000
Description of Derivative Activity Volume Percent	70.00%
Debt Instrument, Interest Rate, Stated Percentage						6.55%
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	1,510,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	10,200,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	1,010,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Four	5,300,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	201,200,000
Line of Credit Facility, Remaining Borrowing Capacity	1,240,000,000
Line of Credit Facility, Collateral, Amount	1,200,000,000
Interest Paid, Net	$ 167,400,000	$ 176,300,000	$ 205,900,000
Debt Instrument, Interest Rate, Effective Percentage	3.00%	2.87%