Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Rental expense under operating lease agreements				$ 162
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	[1]	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201712Member
Operating lease ROU assets	$ 552		$ 536
Operating lease liabilities	$ 643		$ 631
Weighted average remaining lease term for operating leases	5 years
Weighted average remaining lease term for finance leases	4 years
Weighted average discount rate for operating leases	3.51%
Weighted average discount rate for finance leases	3.95%
Adjustment upon Adoption
Lessee, Lease, Description [Line Items]
Operating lease ROU assets				$ 615
Operating lease liabilities				$ 630
Maximum
Lessee, Lease, Description [Line Items]
Term length for operating leases	34 years

[1] See Note 3 for further information about the Company's adoption of new credit loss guidance (ASU 2016-13).