Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Revolving Credit Facility [Member]	Sep. 30, 2014 4.5% Senior Notes due 2023 [Member]	Sep. 30, 2014 Note Payable [Member]	Sep. 30, 2014 8.25% Senior Notes due 2019 (1)	Sep. 30, 2014 8.25% Senior Notes due 2019 (1)	Sep. 30, 2014 7.375% Senior Notes due 2020	Sep. 30, 2014 7.125% Senior Notes due 2021	Sep. 30, 2014 5% Senior Notes due 2022	Sep. 30, 2014 3.8% Senior Notes due 2024	Sep. 30, 2014 4.9% Senior Notes due 2044	Sep. 30, 2014 Carrying Amount	May 19, 2014 Carrying Amount	Dec. 31, 2013 Carrying Amount	Sep. 30, 2014 Carrying Amount 8.25% Senior Notes due 2019 (1)	Dec. 31, 2013 Carrying Amount 8.25% Senior Notes due 2019 (1)	Sep. 30, 2014 Carrying Amount 7.375% Senior Notes due 2020	Dec. 31, 2013 Carrying Amount 7.375% Senior Notes due 2020	Sep. 30, 2014 Carrying Amount 7.125% Senior Notes due 2021	Dec. 31, 2013 Carrying Amount 7.125% Senior Notes due 2021	Sep. 30, 2014 Carrying Amount 5% Senior Notes due 2022	Dec. 31, 2013 Carrying Amount 5% Senior Notes due 2022	Sep. 30, 2014 Carrying Amount 3.8% Senior Notes due 2024	Dec. 31, 2013 Carrying Amount 3.8% Senior Notes due 2024	Sep. 30, 2014 Carrying Amount 4.9% Senior Notes due 2044	Dec. 31, 2013 Carrying Amount 4.9% Senior Notes due 2044
Debt Instrument [Line Items]
Line of credit facility, amount outstanding																$ 0	$ 1,010,000,000	$ 275,000,000
Line of credit facility, maturity date			May 16, 2019
Aggregate amount of lender commitments on credit facility	1,750,000,000		1,750,000,000
Line of Credit Facility, Maximum Borrowing Capacity	4,000,000,000		4,000,000,000
Line of credit facility, unused commitments						1,750,000,000
Line of credit facility, commitment fee percentage, per annum	0.225%
Credit Facility Debt to Capitalization Ratio Covenant Requirement			0.65
Notes Payable								22,000,000								16,967,000		18,470,000
Loan term								10 years
Debt Instrument, stated interest rate							4.50%	3.14%	8.25%	8.25%	7.375%	7.125%	5.00%	3.80%	4.90%
Debt Instrument, Maturity Date								Feb. 26, 2022
Current portion of long-term debt	2,062,000		2,062,000		2,011,000
Senior notes														1,000,000,000	700,000,000				0	298,305,000	198,809,000	198,695,000	400,000,000	400,000,000	2,023,568,000	2,025,362,000	996,548,000	0	698,030,000	0
Debt Instrument, Maturity Date, Description							2023			2019	2020	2021	2022	2024	2044
Proceeds from Debt, Net of Issuance Costs	1,680,000,000
Total Redemption Amount									317,500,000	317,500,000
Loss on Extinguishment of Debt	$ (24,517,000)	$ 0	$ (24,517,000)	$ 0					$ 24,517,000