Debt - Schedule of Long-term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Long-term debt, due within one year	$ 3,516	$ 4,819
Long-term debt, due after one year	12,360	12,676
Total long-term debt	15,876	17,495
Unsecured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	1,161	2,408
Long-term debt, due after one year	9,358	8,654
Total long-term debt	10,519	11,062
Secured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	2,355	2,411
Long-term debt, due after one year	3,002	4,022
Total long-term debt	5,357	6,433
Federal Home Loan Bank advances | Federal Home Loan Bank of Pittsburgh
Debt Instrument [Line Items]
Total long-term debt	$ 3,700	$ 4,200