Background (Details) $ in Millions	3 Months Ended
	Sep. 30, 2019 USD ($) derivative_agreement	Mar. 31, 2019 derivative_agreement	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Book overdraft balance	$ 2			$ 86
Number of new instruments held | derivative_agreement	6	5
Operating lease assets	$ 1,721
Operating lease liabilities	$ 1,770
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets			$ 2,100
Operating lease liabilities			2,200
Retained Earnings | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU			$ 115