Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Other assets	$ 502
Operating lease, liability	636
Operating lease, payments	202
Right-of-use asset obtained in exchange for operating lease liability	$ 232
Operating lease, weighted average remaining lease term	8 years
Operating lease, weighted average discount rate	4.10%
Operating leases, rent expense		$ 213	$ 211
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Other assets				$ 458
Operating lease, liability				$ 574