Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Advertising Expense	$ 54	$ 121	$ 116
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	63	56
Other related Revenue	159	144
Equity Securities without Readily Determinable Fair Value, Amount	8
Revenues	5,402	9,172	9,124
Currency translation adjustment	40	9	(3)	$ 71
Net carrying value of software developed	265	261
Vehicle interest income	12	15	15
Retained risks of liability to third parties	396	441
Workers compensation liabilities	53	56
Operating Costs and Expenses	3,322	4,698	4,639
Costs and Expenses	6,358	8,885	8,857
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(956)	287	267
Income Tax Expense (Benefit)	(272)	(15)	102
Net income	(684)	302	165
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(714)	277	62
Total Assets Exclusive Of Assets Under Vehicle Programs	8,365	9,311
Assets	17,538	23,126
Accounts Payable and Accrued Liabilities, Current	2,034	2,206
Liabilities, Current	2,053	2,225
Other Liabilities, Noncurrent	731	757
Total Liabilities Exclusive Of Liabilities Under Vehicle Programs	9,053	8,538
Income (Loss) from Equity Method Investments	10	5
Proceeds from Sale of Equity Method Investments	64
Gain (Loss) on Sale of Equity Investments	44
Gain on Sale of Investments	4
Operating Lease, Right-of-Use Asset	2,560	2,596
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	765	900	735	$ 901
Customer Loyalty [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred Revenue	34	59	$ 64
Deferred Revenue, Additions	26	17
Deferred Revenue, Revenue Recognized	51	22
Deferred Revenue, Current	17	22
Deferred Revenue, Noncurrent	17	37
Property leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset	2,560	2,596
Vehicle leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset	$ 113	$ 195