Financial Instruments, Derivatives and Hedging Activities Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Sep. 22, 2016
Long-term debt
Carrying amount	$ 1,744	$ 1,850
Long-term debt	1,845	1,929
Carrying Amount of Fair Value Adjustment Hedged Fixed Rate Debt	1	3
Fair value adjustment related to hedged fixed rate debt instrument	1,744	1,850
Senior Notes 3.2 Percent Due October 1, 2026
Long-term debt
Carrying amount	496	496
Long-term debt	$ 492	$ 482
Debt, interest rate (as a percent)	3.20%	3.20%	3.20%
Senior Notes 4.625 Percent Due November 1, 2020
Long-term debt
Carrying amount	$ 398	$ 398
Long-term debt	$ 421	$ 428
Debt, interest rate (as a percent)	4.625%	4.625%
Senior Notes 1.8 Percent Due September 25, 2017
Long-term debt
Carrying amount		$ 299
Long-term debt		$ 301
Debt, interest rate (as a percent)	1.80%	1.80%
Senior Notes 6.0 Percent Due April 15, 2017
Long-term debt
Carrying amount		$ 200
Long-term debt		$ 202
Debt, interest rate (as a percent)	6.00%	6.00%
Senior Notes 5.62 Percent Due March 25, 2020
Long-term debt
Carrying amount	$ 200	$ 200
Long-term debt	$ 212	$ 217
Debt, interest rate (as a percent)	5.62%	5.62%
Term loan credit agreement due April 25, 2019
Long-term debt
Carrying amount	$ 395
Long-term debt	$ 395