Debt - Narrative (Details) (USD $)	3 Months Ended		9 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Sep. 30, 2012
Long-Term Debt Instrument [Line Items]
Number of revolving bank credit facilities used			2
Debt Instrument Margin Rate Range, Minimum			4.50%
Long-term Debt, Gross		$ 12,620,000,000	$ 12,736,000,000
Corporate Revolving Bank Credit Facility
Long-Term Debt Instrument [Line Items]
Borrowing capacity			4,000,000,000
Interest Rate In Addition To Federal Funds Rate			0.50%
Line of Credit Facility, Commitment Fee Percentage			0.50%
Debt Instrument, Covenant Description	4.75 to 1.00	5.00 to 1.00	4.00 to 1.00	6.00 to 1.00
Increase to Applicable Margin, Credit Facility			0.25%
Credit Facility Borrowing Capacity Margin			50.00%
Minimum Collateral Value, Credit Facility			75,000,000
Line of Credit Facility, Amount Outstanding			0
Corporate Revolving Bank Credit Facility | Maximum
Long-Term Debt Instrument [Line Items]
Debt Instrument, Convertible, Effective Interest Rate			2.25%
Long-term Debt			125,000,000
Corporate Revolving Bank Credit Facility | Minimum
Long-Term Debt Instrument [Line Items]
Debt Instrument Margin Rate Range, Minimum			1.50%
Debt Outstanding Principal Amount			50,000,000
Corporate Revolving Bank Credit Facility | Union Bank N.A. | Maximum
Long-Term Debt Instrument [Line Items]
Debt Instrument, Convertible, Effective Interest Rate			1.25%
Corporate Revolving Bank Credit Facility | Union Bank N.A. | Minimum
Long-Term Debt Instrument [Line Items]
Debt Instrument Margin Rate Range, Minimum			0.50%
Oilfield Services Revolving Bank Credit Facility
Long-Term Debt Instrument [Line Items]
Borrowing capacity			500,000,000
Interest Rate In Addition To Federal Funds Rate			0.50%
Line Of Credit Facility Extended Borrowing Capacity			900,000,000
Debt Instrument Interest Rate In Addition To Eurodollar Rate			1.00%
Acceleration of Principal Amount Due, Credit Facility			50,000,000
Line of Credit Facility, Amount Outstanding			285,000,000
Oilfield Services Revolving Bank Credit Facility | In Excess
Long-Term Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding			$ 15,000,000
Oilfield Services Revolving Bank Credit Facility | Bank Of America N.A.
Long-Term Debt Instrument [Line Items]
Debt Instrument Margin Rate Range, Minimum			1.00%
Debt Instrument, Convertible, Effective Interest Rate			1.75%
Oilfield Services Revolving Bank Credit Facility | Bank Of America N.A. | Maximum
Long-Term Debt Instrument [Line Items]
Line of Credit Facility, Commitment Fee Percentage			0.50%
Percentage above LIBOR rate			2.75%
Oilfield Services Revolving Bank Credit Facility | Bank Of America N.A. | Minimum
Long-Term Debt Instrument [Line Items]
Line of Credit Facility, Commitment Fee Percentage			0.375%
Percentage above LIBOR rate			2.00%