Fair Value Measurements - Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2024		Dec. 31, 2023	Jun. 30, 2023	[1]
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	$ 1,611		$ 1,647
Other securities	70		72
Restricted cash and restricted cash equivalents	630	[1]	534	$ 532
U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	12		17
Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	65		66
Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	40		14
Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	161		167
Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,059		1,085
RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	175		180
CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	26		33
CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	73		85
Level 1
Investments, Debt and Equity Securities [Abstract]
Total investment securities	53		54
Restricted cash and restricted cash equivalents	629		534
Level 2
Investments, Debt and Equity Securities [Abstract]
Total investment securities	1,624		1,662
Restricted cash and restricted cash equivalents	1		0
Level 3
Investments, Debt and Equity Securities [Abstract]
Total investment securities	4		3
Restricted cash and restricted cash equivalents	0		0
Fair Value, Measurements, Recurring
Assets
Cash equivalents in mutual funds	164		97
Cash equivalents in securities	48
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,611		1,647
Other securities	70		72
Total investment securities	1,681		1,719
Restricted cash equivalents in mutual funds	623		525
Restricted cash and restricted cash equivalents	1
Total	2,517		2,341
Fair Value, Measurements, Recurring | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	21		22
Fair Value, Measurements, Recurring | U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	12		17
Fair Value, Measurements, Recurring | Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	65		66
Fair Value, Measurements, Recurring | Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	40		14
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	161		167
Fair Value, Measurements, Recurring | Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,059		1,085
Other securities	5		4
Fair Value, Measurements, Recurring | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	175		180
Fair Value, Measurements, Recurring | CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	26		33
Fair Value, Measurements, Recurring | CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	73		85
Other securities	16		18
Fair Value, Measurements, Recurring | Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities	14		16
Fair Value, Measurements, Recurring | Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities	35		34
Fair Value, Measurements, Recurring | Level 1
Assets
Cash equivalents in mutual funds	164		97
Cash equivalents in securities	0
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	6		6
Other securities	47		48
Total investment securities	53		54
Restricted cash equivalents in mutual funds	623		525
Restricted cash and restricted cash equivalents	0
Total	840		676
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		6
Other securities	0		0
Fair Value, Measurements, Recurring | Level 1 | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0		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	14		16
Fair Value, Measurements, Recurring | Level 1 | Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities	33		32
Fair Value, Measurements, Recurring | Level 2
Assets
Cash equivalents in mutual funds	0		0
Cash equivalents in securities	48
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,604		1,640
Other securities	20		22
Total investment securities	1,624		1,662
Restricted cash equivalents in mutual funds	0		0
Total	1,673		1,662
Fair Value, Measurements, Recurring | Level 2 | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	20		22
Fair Value, Measurements, Recurring | Level 2 | U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	12		17
Fair Value, Measurements, Recurring | Level 2 | Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	65		66
Fair Value, Measurements, Recurring | Level 2 | Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	40		14
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	161		167
Fair Value, Measurements, Recurring | Level 2 | Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,052		1,078
Other securities	4		4
Fair Value, Measurements, Recurring | Level 2 | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	175		180
Fair Value, Measurements, Recurring | Level 2 | CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	26		33
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	73		85
Other securities	16		18
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		1
Other securities	3		2
Total investment securities	4		3
Restricted cash equivalents in mutual funds	0		0
Restricted cash and restricted cash equivalents	0
Total	4		3
Fair Value, Measurements, Recurring | Level 3 | Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	1		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		1
Other securities	1		0
Fair Value, Measurements, Recurring | Level 3 | RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0		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.