Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
2023 & 2025 Fixed-to-Floating Interest Rate Swaps | Fair Value Hedging | Designated as Hedging Instrument
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate fair value hedge asset at fair value	$ 27	$ 7
2022 Fixed-to-Floating Interest Rate Swaps | Fair Value Hedging | Designated as Hedging Instrument
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value hedge derivative instrument liabilities at fair value	93	123
Forward Starting Interest Rate Swap | Cash Flow Hedge | Designated as Hedging Instrument
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash flow hedge derivative instrument assets at fair value	0	0
Cash flow hedge derivative instrument liabilities at fair value	0	0
Carrying Value
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Investments at Fair Value	172	214
Total investments at amortized cost	$ 171	$ 218