Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Assets:
Investments	$ 9	$ 7
Foreign Exchange Contracts	5	15
Total Assets at Fair Value	14	22
Liabilities:
Foreign Exchange Contracts	36	11
Total Liabilities at Fair Value	36	11
Fair Value of Long Term Fixed Rate and Variable Rate Debt, Excluding Capital Leases
Carrying amount — liability	5,952	5,611
Fixed Rate Debt, Excluding Capital Leases
Fair Value of Long Term Fixed Rate and Variable Rate Debt, Excluding Capital Leases
Carrying amount — liability	3,550	3,844
Fair value — liability	3,742	4,018
Variable Rate Debt, Excluding Capital Leases
Fair Value of Long Term Fixed Rate and Variable Rate Debt, Excluding Capital Leases
Carrying amount — liability	2,402	1,767
Fair value — liability	2,388	1,765
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Assets:
Investments	9	7
Foreign Exchange Contracts	0	0
Total Assets at Fair Value	9	7
Liabilities:
Foreign Exchange Contracts	0	0
Total Liabilities at Fair Value	0	0
Fair Value of Long Term Fixed Rate and Variable Rate Debt, Excluding Capital Leases
Fair value — liability	4,058	4,291
Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Foreign Exchange Contracts	5	15
Total Assets at Fair Value	5	15
Liabilities:
Foreign Exchange Contracts	36	11
Total Liabilities at Fair Value	36	11
Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Foreign Exchange Contracts	0	0
Total Assets at Fair Value	0	0
Liabilities:
Foreign Exchange Contracts	0	0
Total Liabilities at Fair Value	$ 0	$ 0