Guarantee Arrangements, Pledged Assets and Repurchase Agreements, Collateral Pledged and Remaining Contractual Maturity of Repurchase Agreements Accounted for as Secured Borrowings (Details) - U.S. Treasury, U.S. Government sponsored and U.S. Government agency securities - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	$ 5,300	$ 3,700
Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	2,900	1,400
Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	400	500
31 to 90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	0	700
91 Days to One Year
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	2,000	1,100
Greater Than One Year
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral pledged and remaining contractual maturity of repurchase agreements accounted for as secured borrowings	$ 0	$ 0