Debt - Schedule of Long-term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Long-term debt, due within one year	$ 4,428	$ 4,819
Long-term debt, due after one year	12,037	12,676
Total long-term debt	16,465	17,495
Unsecured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	1,968	2,408
Long-term debt, due after one year	8,610	8,654
Total long-term debt	10,578	11,062
Secured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	2,460	2,411
Long-term debt, due after one year	3,427	4,022
Total long-term debt	5,887	6,433
Federal Home Loan Bank advances | Federal Home Loan Bank of Pittsburgh
Debt Instrument [Line Items]
Total long-term debt	$ 3,900	$ 4,200