The table below details the activity of the allowance for doubtful accounts, deferred tax asset valuation allowance, and insurance reserves (in millions):


	Balance at Beginning of Period		Additions (1), (2)		Deductions (2)		Balance at End of Period
Year Ended December 31, 2021
Allowance for doubtful accounts	$	55	$	246	$	(250)	$	51
Deferred tax asset valuation allowance	$	13,410	$	571	$	(61)	$	13,920
Insurance reserves	$	3,466	$	1,696	$	(1,174)	$	3,988
Year Ended December 31, 2022
Allowance for doubtful accounts	$	51	$	286	$	(257)	$	80
Deferred tax assets valuation allowance	$	13,920	$	2,204	$	(2,153)	$	13,971
Insurance reserves	$	3,988	$	2,128	$	(1,396)	$	4,720
Year Ended December 31, 2023
Allowance for doubtful accounts	$	80	$	245	$	(234)	$	91
Deferred tax assets valuation allowance	$	13,971	$	81	$	(107)	$	13,945
Insurance reserves	$	4,720	$	3,544	$	(1,526)	$	6,738

(1) Additions to insurance reserves include $69 million, $152 million and $158 million for the years ended December 31, 2021, 2022 and 2023 respectively, for changes in estimates resulting from new developments in prior period claims. Additions to insurance reserves also include $374 million for the year ended December 31, 2021 for reserves assumed in connection with a loss portfolio transfer reinsurance agreement. For additional information on the loss portfolio transfer reinsurance agreement, see Note 1 – Description of Business and Summary of Significant Accounting Policies.

(2) For the year ended December 31, 2021, the increase in the valuation allowance was primarily attributable to a tax rate increase in the Netherlands, an increase in U.S. federal, state and Netherlands deferred tax assets resulting from the loss from operations, and tax credits generated during the year, offset partially by the release of the valuation allowance due to deferred tax liabilities recorded as a result of the acquisitions providing an additional source of taxable income to support the realizability of pre-existing deferred tax assets.

For the year ended December 31, 2022, the increase in the valuation allowance was primarily attributable to an increase in deferred tax assets resulting from the loss from operations, offset by the deferred tax impact from the transfer of certain intangible assets among our wholly-owned subsidiaries.