Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases
Stockholders' equity	$ 10,063			$ 9,796
Operating leases, existence of option to extend	true
Finance leases, existence of option to extend	true
Lease liabilities	$ 854
Operating lease right of use assets	$ 858
Lease, Practical Expedients, Package [true false]	true
Lease, Practical Expedient, Use of Hindsight [true false]	false
ASU 2016-02 Leases
Leases
Lease liabilities		$ 800
Operating lease right of use assets		$ 800
Adjustment | ASU 2016-02 Leases
Leases
Lease liabilities			$ 800
Operating lease right of use assets			800
Retained Earnings | Adjustment | ASU 2016-02 Leases
Leases
Stockholders' equity			$ 14