Bank Financing and Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 31, 2016	Jul. 31, 2015	Jan. 31, 2015
Debt Disclosure [Abstract]
Net unamortized discount on senior debt	$ 45,000,000	$ 21,000,000
Increase in the carrying value of debt relating to previously settled fair value hedges	14,000,000	14,000,000
Loss on early extinguishment of debt	0	352,000,000	$ 0
Unamortized deferred financing costs	44,000,000	34,000,000
Debt Instrument [Line Items]
Commercial paper	0	616,000,000
Carrying value of senior debt	8,370,000,000	6,400,000,000
Capital lease obligations	83,000,000	97,000,000
Face value of debt	8,520,000,000	7,150,000,000
Face amount of debt repurchased		1,170,000,000
Total debt	8,448,000,000	7,112,000,000
Less current portion	222,000,000	20,000,000
Total long-term debt, net of current portion	8,226,000,000	6,476,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2016	200,000,000
2017	400,000,000
2018	300,000,000
2019	600,000,000
2020	500,000,000
2021 and Thereafter	6,440,000,000
Redemption or Repurchase Prior To Maturity[Member]
Debt Instrument [Line Items]
Face amount of debt repurchased		1,070,000,000
Total Debt Issuances [Member]
Debt Instrument [Line Items]
Face value of debt		1,750,000,000
Senior Debentures due 2016 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 200,000,000	200,000,000
Stated interest rate	7.625%
Senior Debentures due 2016 [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Stated interest rate				7.625%
Face amount of debt repurchased				$ 200,000,000
Senior Notes due 2017 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 398,000,000	397,000,000
Stated interest rate	1.95%
Senior Notes due 2018 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 309,000,000	313,000,000
Stated interest rate	4.625%
Senior Notes due 2019 B [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 609,000,000	$ 596,000,000
Stated interest rate	2.30%	2.30%
Face value of debt		$ 600,000,000
Senior Notes due 2020 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 498,000,000	498,000,000
Stated interest rate	5.75%
Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 299,000,000	299,000,000
Stated interest rate	4.30%
Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 694,000,000	693,000,000
Stated interest rate	3.375%
Debentures due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 186,000,000	186,000,000
Stated interest rate	7.875%
Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 46,000,000	46,000,000
Stated interest rate	7.125%
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 596,000,000	595,000,000
Stated interest rate	3.70%
Senior Debentures due 2030 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 833,000,000	833,000,000
Stated interest rate	7.875%
Senior Debentures due 2033 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 425,000,000	425,000,000
Stated interest rate	5.50%
Senior Notes due 2040 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 297,000,000	297,000,000
Stated interest rate	5.90%
Senior Notes due 2042 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 484,000,000	484,000,000
Stated interest rate	4.85%
Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 538,000,000	537,000,000
Stated interest rate	4.90%
Senior Notes Due 2025 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 585,000,000	0
Stated interest rate						3.50%
Face value of debt						$ 600,000,000
Senior Notes Due 2045 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	587,000,000	0
Stated interest rate						4.60%
Face value of debt						$ 600,000,000
Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 781,000,000	$ 0
Stated interest rate					4.00%
Face value of debt					$ 800,000,000