Employee Benefit Plans - Defined Contribution Plan (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) age	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost | $	$ 282	$ 252	$ 234
Associate Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, age eligible to participate | age	18