Leases - Operating ROU Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease ROU assets	[1]	$ 527	$ 719
Operating lease liabilities		$ 625	$ 783
Weighted-average remaining lease term		6 years 9 months 18 days	7 years 2 months 12 days
Weighted-average discount rate (percent)		3.00%	3.10%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssets
Operating Lease, Liability, Statement of Financial Position [Extensible List]			us-gaap:OtherLiabilities

[1] Reported net of level lease adjustments and accumulated impairment losses.