Related Party Transactions - Summary of Loans (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
HMUS [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	$ 1,755	$ 1,088
HNAH [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	1,000	0
Other short-term affiliate lending [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	102	12
HSBC Affiliates [Member]
Related Party Transaction [Line Items]
Loans receivable from related parties	$ 2,857	$ 1,100