Related Party Transactions - Summary of Loans (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
HMUS [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	$ 1,591	$ 1,088
Other short-term affiliate lending [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	61	12
HSBC Affiliates [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	$ 1,652	$ 1,100