Fair Value Measurements - Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		$ 1,647	$ 1,729
Other securities		72	71
Restricted cash and restricted cash equivalents	[1]	534	461	$ 476
U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		17	16
Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		66	66
Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1,085	1,137
RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		180	192
CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		33	35
CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		85	86
Level 1
Investments, Debt and Equity Securities [Abstract]
Total investment securities		54	51
Restricted cash and restricted cash equivalents		534	450
Level 2
Investments, Debt and Equity Securities [Abstract]
Total investment securities		1,662	1,744
Restricted cash and restricted cash equivalents		0	11
Level 3
Investments, Debt and Equity Securities [Abstract]
Total investment securities		3	5
Restricted cash and restricted cash equivalents		0	0
Fair Value, Measurements, Recurring
Assets
Cash equivalents in mutual funds		97	77
Cash equivalents in securities			17
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1,647	1,729
Other securities		72	71
Total investment securities		1,719	1,800
Restricted cash equivalents in mutual funds		525	445
Restricted cash and restricted cash equivalents			11
Total		2,341	2,350
Fair Value, Measurements, Recurring | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities		22	23
Fair Value, Measurements, Recurring | U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		17	16
Fair Value, Measurements, Recurring | Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		66	66
Fair Value, Measurements, Recurring | Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		14	55
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		167	142
Fair Value, Measurements, Recurring | Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1,085	1,137
Other securities		4	6
Fair Value, Measurements, Recurring | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		180	192
Other securities			1
Fair Value, Measurements, Recurring | CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		33	35
Fair Value, Measurements, Recurring | CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		85	86
Other securities		18	16
Fair Value, Measurements, Recurring | Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities		16	15
Fair Value, Measurements, Recurring | Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities		34	33
Fair Value, Measurements, Recurring | Level 1
Assets
Cash equivalents in mutual funds		97	77
Cash equivalents in securities			0
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		6	5
Other securities		48	46
Total investment securities		54	51
Restricted cash equivalents in mutual funds		525	445
Restricted cash and restricted cash equivalents			0
Total		676	573
Fair Value, Measurements, Recurring | Level 1 | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities		0	0
Fair Value, Measurements, Recurring | Level 1 | U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 1 | Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 1 | Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		6	5
Other securities		0	0
Fair Value, Measurements, Recurring | Level 1 | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Other securities			0
Fair Value, Measurements, Recurring | Level 1 | CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 1 | CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Other securities		0	0
Fair Value, Measurements, Recurring | Level 1 | Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities		16	15
Fair Value, Measurements, Recurring | Level 1 | Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities		32	31
Fair Value, Measurements, Recurring | Level 2
Assets
Cash equivalents in mutual funds		0	0
Cash equivalents in securities			17
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1,640	1,721
Other securities		22	23
Total investment securities		1,662	1,744
Restricted cash equivalents in mutual funds		0	0
Restricted cash and restricted cash equivalents			11
Total		1,662	1,772
Fair Value, Measurements, Recurring | Level 2 | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities		22	23
Fair Value, Measurements, Recurring | Level 2 | U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		17	16
Fair Value, Measurements, Recurring | Level 2 | Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		66	66
Fair Value, Measurements, Recurring | Level 2 | Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		14	55
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		167	142
Fair Value, Measurements, Recurring | Level 2 | Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1,078	1,129
Other securities		4	6
Fair Value, Measurements, Recurring | Level 2 | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		180	192
Other securities			1
Fair Value, Measurements, Recurring | Level 2 | CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		33	35
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		85	86
Other securities		18	16
Fair Value, Measurements, Recurring | Level 2 | Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities		0	0
Fair Value, Measurements, Recurring | Level 2 | Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities		0	0
Fair Value, Measurements, Recurring | Level 3
Assets
Cash equivalents in mutual funds		0	0
Cash equivalents in securities			0
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1	3
Other securities		2	2
Total investment securities		3	5
Restricted cash equivalents in mutual funds		0	0
Restricted cash and restricted cash equivalents			0
Total		3	5
Fair Value, Measurements, Recurring | Level 3 | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities		0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 3 | Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 3 | Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		1	3
Other securities		0	0
Fair Value, Measurements, Recurring | Level 3 | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Other securities			0
Fair Value, Measurements, Recurring | Level 3 | CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Fair Value, Measurements, Recurring | Level 3 | CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities		0	0
Other securities		0	0
Fair Value, Measurements, Recurring | Level 3 | Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities		0	0
Fair Value, Measurements, Recurring | Level 3 | Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities		$ 2	$ 2

[1] Restricted cash and restricted cash equivalents primarily represent funds required to be used for future debt payments relating to our secured transactions.