Summary of Significant Accounting Policies - Leases (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 2,426	$ 2,250	$ 2,000
Operating lease liabilities	2,435	2,264
Retained earnings	$ 159	$ 261
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease liabilities			$ 2,000
Cumulative Effect, Period of Adoption, Adjustment
Lessee, Lease, Description [Line Items]
Retained earnings				$ 149