Related Party Transactions - Summary of Loans (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
HMUS [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	$ 1,088	$ 2,296
Other short-term affiliate lending [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	12	47
HSBC Affiliates [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	$ 1,100	$ 2,343