Schedule of Long-term Debt Outstanding (Details) - USD ($)	1 Months Ended		6 Months Ended
	Oct. 31, 2014	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Dec. 31, 2008
Debt Instrument [Line Items]
Total long-term debt			$ 3,823,000,000	$ 3,825,000,000
Senior Notes
Debt Instrument [Line Items]
Total long-term debt			$ 3,823,000,000	3,825,000,000
Proceeds from issuance of debt, net of underwriters' discount and commission and offering expenses		$ 1,730,000,000
Redemption price, percentage			100.00%
Unamortized discount (premium)			$ 30,000,000	$ 32,000,000	$ 103,000,000
Senior Notes | 6.45% Senior Notes due June 2016
Debt Instrument [Line Items]
Redemption price, percentage	100.00%
Extinguishment of debt, amount paid	$ 560,000,000
Loss on extinguishment of debt	37,000,000
Unamortized discount (premium)	$ 12,000,000
Senior Notes | $500 million, 7.20% due June 15, 2018
Debt Instrument [Line Items]
Stated interest rate			7.20%	7.20%
Face amount			$ 500,000,000	$ 500,000,000
Total long-term debt			$ 504,000,000	$ 504,000,000
Senior Notes | $300 million, 6.30% due August 1, 2018
Debt Instrument [Line Items]
Stated interest rate			6.30%	6.30%
Face amount			$ 300,000,000	$ 300,000,000
Total long-term debt			$ 310,000,000	$ 312,000,000
Senior Notes | $400 million, 2.625% due October 1, 2019
Debt Instrument [Line Items]
Stated interest rate			2.625%	2.625%
Face amount			$ 400,000,000	$ 400,000,000
Total long-term debt			$ 400,000,000	$ 400,000,000
Senior Notes | $600 million, 3.15% due December 1, 2022
Debt Instrument [Line Items]
Stated interest rate			3.15%	3.15%
Face amount			$ 600,000,000	$ 600,000,000
Total long-term debt			$ 598,000,000	$ 598,000,000
Senior Notes | $600 million, 3.85% due October 1, 2024
Debt Instrument [Line Items]
Stated interest rate			3.85%	3.85%
Face amount			$ 600,000,000	$ 600,000,000
Total long-term debt			$ 599,000,000	$ 599,000,000
Senior Notes | $250 million, 8.15% due June 15, 2038
Debt Instrument [Line Items]
Stated interest rate			8.15%	8.15%
Face amount			$ 250,000,000	$ 250,000,000
Total long-term debt			$ 266,000,000	$ 266,000,000
Senior Notes | $400 million, 4.625% due December 1, 2042
Debt Instrument [Line Items]
Stated interest rate			4.625%	4.625%
Face amount			$ 400,000,000	$ 400,000,000
Total long-term debt			$ 400,000,000	$ 400,000,000
Senior Notes | $750 million, 4.95% due October 1, 2044
Debt Instrument [Line Items]
Stated interest rate			4.95%	4.95%
Face amount			$ 750,000,000	$ 750,000,000
Total long-term debt			$ 746,000,000	$ 746,000,000