Loans, Lending Commitments and Related Allowance for Credit Losses - Past Due Status for Loans Held for Investment Modified in the Last 12 Months (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	$ 204,935	$ 204,554
Total
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	45
30-89 Days Past Due
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	0
90+ Days Past Due
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	45
Commercial real estate
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	8,689	$ 8,678
Commercial real estate | Total
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	45
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	0
Commercial real estate | 90+ Days Past Due
Financing Receivable, Modified, Subsequent Default [Line Items]
Total loans	$ 45