Debt - Schedule of Long-term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Long-term debt, due within one year	$ 3,506	$ 4,819
Long-term debt, due after one year	13,243	12,676
Total long-term debt	16,749	17,495
Unsecured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	1,088	2,408
Long-term debt, due after one year	9,994	8,654
Total long-term debt	11,082	11,062
Secured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	2,418	2,411
Long-term debt, due after one year	3,249	4,022
Total long-term debt	5,667	6,433
Federal Home Loan Bank advances | Federal Home Loan Bank of Pittsburgh
Debt Instrument [Line Items]
Total long-term debt	$ 7,100	$ 4,200