Description of Business, Basis of Presentation, and Significant Accounting Policies - Narrative (Details)		3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($)	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) segment	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2024 USD ($)	Jan. 01, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of loan portfolio segments | segment			4
Financing receivable, allowance for credit loss, excluding accrued interest, forecast period	12 months	24 months
Financing receivable, allowance for credit loss, excluding accrued interest, reversion period	24 months	12 months
Operating lease impairment loss			$ 0	$ 0	$ 0
Impairment, long-lived assets			0	0	$ 0
Reduction to opening retained earnings	$ (111,000,000)	$ (208,000,000)	$ (270,000,000)	$ (91,000,000)		$ (284,000,000)		$ (148,000,000)	$ 15,000,000	$ 205,000,000
Adjustments | Accounting Standards Update 2023-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction to opening retained earnings							$ 2,000,000
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life			3 years
Minimum | Capitalized software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life			3 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life			30 years
Maximum | Capitalized software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life			5 years