Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Advertising
Advertising expenses	$ 704	$ 665	$ 626
Pension and Post-Employment Benefits
Amortization period of differences between the expected long-term return on plan assets and the actual return	5 years