Summary of Significant Accounting and Reporting Policies - Significant Accounting and Reporting Policies (Details) $ in Millions	Jun. 30, 2023	Jan. 01, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jan. 01, 2023 USD ($)	Dec. 31, 2022 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings			$ (22,997)		$ (21,689)
Secured Overnight Financing Rate (SOFR)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tenor spread adjustment on basis rate (as a percent)	0.0026161
Large Commercial Loans and Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Larger commercial loans, subject to impairment review			$ 1
Cumulative Effect, Period of Adoption, Adjustment | Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		$ 10
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2022-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in ACL				$ 49
Retained earnings				$ (37)