The following table presents a reconciliation of the Company's beginning and ending gross reserve for losses and loss expenses and net reserve for unpaid losses and loss expenses:


	Three months ended March 31,
	2023		2022

Gross reserve for losses and loss expenses, beginning of period	$	15,168,863	$	14,653,094
Less reinsurance recoverable on unpaid losses and loss expenses, beginning of period	(5,831,172)		(5,017,611)
Net reserve for unpaid losses and loss expenses, beginning of period	9,337,691		9,635,483

Net incurred losses and loss expenses related to:
Current year	724,680		741,655
Prior years	(4,038)		(8,956)
	720,642		732,699

Net paid losses and loss expenses related to:
Current year	(38,662)		(32,477)
Prior years	(574,538)		(750,969)
	(613,200)		(783,446)

Foreign exchange and other	46,094		(71,661)

Net reserve for unpaid losses and loss expenses, end of period	9,491,227		9,513,075
Reinsurance recoverable on unpaid losses and loss expenses, end of period	5,823,417		4,957,080
Gross reserve for losses and loss expenses, end of period	$	15,314,644	$	14,470,155

The Company writes business with loss experience generally characterized as low frequency and high severity in nature, which can result in volatility in its financial results. During the three months ended March 31, 2023, the Company recognized catastrophe and weather-related losses, net of reinstatement premiums, of $38 million (2022: $60 million).

At March 31, 2023, net reserves for losses and loss expenses included estimated amounts for numerous catastrophe events. The magnitude and complexity of losses arising from certain of these events inherently increase the level of uncertainty and, therefore, the level of management judgment involved in arriving at estimated net reserves for losses and loss expenses. These events include New Zealand floods and Cyclone Gabrielle in 2023, Hurricane Ian, Winter Storm Elliot, June European Convective Storms, the Russia-Ukraine war and COVID-19 in 2022, Hurricane Ida, U.S. Winter Storms Uri and Viola and July European Floods in 2021, and the COVID-19 pandemic, Hurricanes Laura, Sally, Zeta and Delta, the Midwest derecho and wildfires across the West Coast of the United States in 2020. As a result, actual losses for these events may ultimately differ materially from current estimates.

The Company's net favorable prior year reserve development arises from changes to estimates of losses and loss expenses related to loss events that occurred in previous calendar years. The following table presents net prior year reserve development by segment:


	Net Favorable Prior Year Reserve Development
	Insurance		Reinsurance		Total

Three months ended March 31, 2023	$	1,041	$	2,997	$	4,038
Three months ended March 31, 2022	$	7,062	$	1,894	$	8,956

Insurance segment

Expected claims tail

Short

Medium

Long

Lines of business

Property

Accident and health

Marine and aviation

Cyber

Professional lines

Credit and political risk

Liability


	Three months ended March 31,
	2023		2022
	Favorable (Adverse)		Favorable (Adverse)

Property	$	5,900	$	8,060
Accident and health	(304)		3,632
Marine and aviation	13,221		14,647
Cyber	8,452		(687)
Professional lines	(12,594)		(5,936)
Credit and political risk	4,519		895
Liability	(18,153)		(13,549)
Total	$	1,041	$	7,062

•$13 million of net favorable prior year reserve development on marine and aviation business primarily due to better than expected loss emergence mainly related to 2021 and 2022 accident years.

•$8 million of net favorable prior year reserve development on cyber business primarily due to better than expected loss emergence mainly related to 2019 and older accident years.

•$6 million of net favorable prior year reserve development on property business primarily due to better than expected loss emergence attributable to 2018 and older accident years, partially offset by reserve strengthening related to the 2021 accident year.

•$5 million of net favorable prior year reserve development on credit and political risk business primarily due to a decrease in the loss estimate attributable to a specific large claim related to the 2020 accident year and better than expected loss emergence attributable to the Lloyds book of business related to several accident years.

•$18 million of net adverse prior year reserve development on liability business primarily due to reserve strengthening within the U.S. primary casualty book of business mainly related to the 2015, 2018 and 2021 accident years.

•$13 million of net adverse prior year reserve development on professional lines business primarily due to reserve strengthening within the U.S. commercial management solutions book of business mainly related to several accident years and U.S. financial institutions book of business mainly related to the 2018 accident year.

•$15 million of net favorable prior year reserve development on marine and aviation business primarily due to better than expected loss emergence attributable to the marine cargo and marine offshore energy books of business mainly related to the 2018 and 2021 accident years.

•$8 million of net favorable prior year reserve development on property business primarily due to decreases in loss estimates attributable to specific large claims related to the 2017 accident year, and better than expected loss emergence attributable to 2018 catastrophe events.

•$14 million of net adverse prior year reserve development on liability business primarily due to reserve strengthening within the program book of business mainly related to the 2016 and 2018 accident years and an increase in the loss estimate attributable to a specific large claim related to the 2017 accident year.

•$6 million of net adverse prior year reserve development on professional lines business primarily due to increases in loss estimates attributable to specific large claims related to the 2015 and 2017 accident years, and reserve strengthening within runoff lines of business mainly related to the 2016 and 2018 accident years.

Reinsurance segment

Expected claims tail

Short

Medium

Long

Lines of business

Accident and health

Agriculture

Marine and aviation

Professional lines

Credit and surety

Motor

Liability

Run-off lines

Catastrophe

Property

Engineering


	Three months ended March 31,
	2023		2022
	Favorable (Adverse)		Favorable (Adverse)

Accident and health	$	6,988	$	(499)
Agriculture	11,891		1,231
Marine and aviation	(250)		497
Professional lines	(3,225)		(24,522)
Credit and surety	(546)		7,465
Motor	(17,122)		(1,730)
Liability	(32,853)		(4,105)
Run-off lines
Catastrophe	31,058		(246)
Property	6,883		22,539
Engineering	173		1,264
Total run-off lines	38,114		23,557
Total	$	2,997	$	1,894

•$33 million of net adverse development on liability business primarily due to reserve strengthening to reflect increased estimates of future loss trend due to inflation, increases in loss estimates attributable to one large claim within the European book of business related to the 2021 accident year and reserve strengthening within the U.S. proportional book of business related to 2019 and older accident years.

•$7 million of net favorable prior year reserve development on credit and surety business primarily due to better than expected loss emergence related to recent accidents years.

•$25 million of net adverse prior year development on professional lines business primarily due to an increase in loss estimates attributable to one cedant related to the 2016 to 2018 accident years and a specific large claim related to the 2017 accident year.

•$4 million of net adverse prior year development on liability business primarily due to an increase in loss estimates attributable to a specific large claim related to the 2018 accident year.

•$23 million of net favorable prior year development on property business primarily due to better than expected loss emergence attributable to 2018, 2019 and 2021 catastrophe events, and an aggregate excess of loss treaty.