Unpaid losses and loss expenses (Tables)

12 Months Ended

Dec. 31, 2020

Liability for Claims and Claims Adjustment Expense [Abstract]

Schedule Of Unpaid Losses And Loss Expenses Roll Forward

Chubb establishes reserves for the estimated unpaid ultimate liability for losses and loss expenses under the terms of its policies and agreements. Reserves include estimates for both claims that have been reported and for IBNR claims, and include estimates of expenses associated with processing and settling these claims. Reserves are recorded in Unpaid losses and loss expenses in the consolidated balance sheets. While we believe that our reserves for unpaid losses and loss expenses at December 31, 2020 are adequate, new information or trends may lead to future developments in incurred loss and loss expenses significantly greater or less than the reserves provided. Any such revisions could result in future changes in estimates of losses or reinsurance recoverable and would be reflected in our results of operations in the period in which the estimates are changed.

The following table presents a reconciliation of beginning and ending Unpaid losses and loss expenses:

	Year Ended December 31
(in millions of U.S. dollars)	2020		2019		2018
Gross unpaid losses and loss expenses, beginning of year	$	62,690	$	62,960	$	63,179
Reinsurance recoverable on unpaid losses (1)	(14,181)		(14,689)		(14,014)
Net unpaid losses and loss expenses, beginning of year	48,509		48,271		49,165
Net losses and loss expenses incurred in respect of losses occurring in:
Current year	22,124		19,575		19,048
Prior years (2)	(414)		(845)		(981)
Total	21,710		18,730		18,067
Net losses and loss expenses paid in respect of losses occurring in:
Current year	7,782		7,894		7,544
Prior years	9,652		10,579		10,796
Total	17,434		18,473		18,340
Foreign currency revaluation and other	379		(19)		(621)
Net unpaid losses and loss expenses, end of year	53,164		48,509		48,271
Reinsurance recoverable on unpaid losses (1)	14,647		14,181		14,689
Gross unpaid losses and loss expenses, end of year	$	67,811	$	62,690	$	62,960

(1)     Net of valuation allowance for uncollectible reinsurance.

(2)    Relates to prior period loss reserve development only and excludes prior period development related to reinstatement premiums, expense adjustments and earned premiums totaling $19 million, $53 million, and $85 million for 2020, 2019, and 2018, respectively.

Reconciliation of Claims Development to Liability [Table Text Block]

The following table presents a reconciliation of the loss development tables to the liability for unpaid losses and loss expenses in the consolidated balance sheet:

Reconciliation of Reserve Balances to Liability for Unpaid Loss and Loss Expenses
(in millions of U.S. dollars)	December 31, 2020
Presented in the loss development tables:
North America Commercial P&C Insurance — Workers' Compensation	$	9,600
North America Commercial P&C Insurance — Liability	17,441
North America Commercial P&C Insurance — Other Casualty	2,124
North America Commercial P&C Insurance — Non-Casualty	2,491
North America Personal P&C Insurance	3,025
Overseas General Insurance — Casualty	6,832
Overseas General Insurance — Non-Casualty	2,725
Global Reinsurance — Casualty	1,200
Global Reinsurance — Non-Casualty	312
Excluded from the loss development tables:
Other	4,742
Net unpaid loss and allocated loss adjustment expense	50,492
Ceded unpaid loss and allocated loss adjustment expense:
North America Commercial P&C Insurance — Workers' Compensation	$	1,461
North America Commercial P&C Insurance — Liability	5,743
North America Commercial P&C Insurance — Other Casualty	564
North America Commercial P&C Insurance — Non-Casualty	1,380
North America Personal P&C Insurance	141
Overseas General Insurance — Casualty	2,426
Overseas General Insurance — Non-Casualty	1,686
Global Reinsurance — Casualty	29
Global Reinsurance — Non-Casualty	104
Other	1,153
Ceded unpaid loss and allocated loss adjustment expense	14,687
Unpaid loss and loss expense on other than short-duration contracts (1)	1,109
Unpaid unallocated loss adjustment expenses	1,523
Unpaid losses and loss expenses	$	67,811

(1)     Primarily includes the claims reserve of our International A&H business and Life Insurance segment reserves.

Claims Development tables [Table Text Block]

This product line has a substantial geographic spread and a broad mix across industries. Types of coverage include risk management business predominantly with high deductible policies, loss sensitive business (i.e., retrospectively-rated policies), business fronted for captives, as well as excess and primary guaranteed cost coverages.

The triangle below shows all loss and allocated expense development for the workers' compensation product line. In our prior period development disclosure, we exclude any loss development where there is a directly related premium adjustment. For workers' compensation, changes in the exposure base due to payroll audits will drive changes in ultimate losses. In addition, we record involuntary pool assumptions (premiums and losses) on a lagged basis. Both of these items will influence the development in the triangle, particularly the first prior accident year, and are included in the reconciliation table presented on page F-58.

North America Commercial P&C Insurance — Workers' Compensation — Long-tail (continued)
Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	1,037	$	1,030		$	1,046	$	1,049	$	1,053	$	1,022	$	1,012	$	1,009	$	988	$	973	$	208	45
2012			1,050			1,011		1,030		1,040		1,011		989		986		977		953		234		44
2013						1,109		1,108		1,122		1,127		1,086		1,073		1,037		1,014		280		43
2014								1,207		1,201		1,217		1,215		1,163		1,100		1,073		347		45
2015										1,282		1,259		1,276		1,279		1,217		1,154		419		50
2016												1,367		1,361		1,383		1,378		1,269		530		51
2017														1,413		1,380		1,399		1,393		723		50
2018																1,359		1,361		1,379		709		51
2019																		1,391		1,384		767		47
2020																				1,367		1,086		24
Total																				$	11,959

Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	119	$	294		$	411	$	484	$	533	$	567	$	595	$	616	$	640	$	654
2012			111			271		365		436		486		532		574		592		612
2013						107		286		422		506		553		587		616		633
2014								113		295		410		484		532		566		599
2015										116		301		418		501		564		606
2016												122		326		452		529		584
2017														120		313		437		516
2018																130		329		451
2019																		143		341
2020																				111
Total																				$	5,107

Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	2,748
Accident years 2011 - 2020 from tables above	6,852
All Accident years	$	9,600

North America Commercial P&C Insurance — Liability — Long-tail

This line consists of primary and excess liability exposures, including medical liability and professional lines, including directors and officers (D&O) liability, errors and omissions (E&O) liability, employment practices liability (EPL), fidelity bonds, and fiduciary liability.

The primary and excess liability business represents the largest part of these exposures. The former includes both monoline and commercial package liability. The latter includes a substantial proportion of commercial umbrella, excess and high excess business, where loss activity can produce significant volatility in the loss triangles at later ages within an accident year (and sometimes across years) due to the size of the limits afforded and the complex nature of the underlying losses.

This line includes management and professional liability products provided to a wide variety of clients, from national accounts to small firms along with private and not-for-profit organizations, distributed through brokers, agents, wholesalers and MGAs. Many of these coverages, particularly D&O and E&O, are typically written on a claims-made form. While most of the coverages are underwritten on a primary basis, there are significant amounts of excess exposure with large policy limits.

Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	3,500	$	3,586		$	3,630	$	3,665	$	3,593	$	3,498	$	3,384	$	3,316	$	3,193	$	3,143	$	226	25
2012			3,552			3,628		3,613		3,565		3,524		3,426		3,331		3,235		3,235		353		25
2013						3,547		3,542		3,543		3,533		3,430		3,216		3,122		2,964		317		25
2014								3,535		3,586		3,674		3,717		3,656		3,470		3,346		572		25
2015										3,560		3,709		3,819		3,976		3,943		3,736		855		27
2016												3,534		3,595		3,692		3,805		3,799		962		27
2017														3,322		3,499		3,581		3,631		1,475		27
2018																3,375		3,494		3,696		1,737		28
2019																		3,452		3,628		2,381		28
2020																				4,098		3,695		24
Total																				$	35,276

Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	160	$	652		$	1,209	$	1,805	$	2,214	$	2,477	$	2,659	$	2,741	$	2,827	$	2,863
2012			166			656		1,172		1,680		2,092		2,326		2,502		2,619		2,688
2013						130		548		1,192		1,597		2,007		2,232		2,374		2,465
2014								164		679		1,250		1,804		2,202		2,442		2,584
2015										138		605		1,206		1,856		2,291		2,533
2016												171		663		1,336		1,975		2,334
2017														161		617		1,162		1,701
2018																190		754		1,303
2019																		176		671
2020																				152
Total																				$	19,294

North America Commercial P&C Insurance — Liability — Long-tail (continued)
Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	1,459
Accident years 2011 - 2020 from tables above	15,982
All Accident years	$	17,441

This product line consists of the remaining commercial casualty coverages such as automobile liability and aviation. There is also a small portion of commercial multi-peril (CMP) business in accident years 2014 and prior. The paid and reported data are impacted by some catastrophe loss activity primarily on the CMP exposures just noted.

Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	581	$	590		$	581	$	549	$	533	$	525	$	517	$	511	$	513	$	503	$	13	16
2012			634			606		577		561		520		519		509		507		505		2		16
2013						527		531		523		516		469		462		462		458		21		18
2014								595		583		581		597		555		539		539		25		17
2015										487		470		502		515		458		455		35		15
2016												504		502		527		524		481		61		16
2017														532		566		577		616		118		17
2018																536		564		575		198		17
2019																		606		637		284		16
2020																				646		517		9
Total																				$	5,415

North America Commercial P&C Insurance — Other-Casualty — Long-tail (continued)
Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	86	$	235		$	341	$	400	$	437	$	461	$	466	$	480	$	486	$	486
2012			69			223		320		387		435		470		487		493		502
2013						69		197		271		348		385		411		419		426
2014								80		220		318		391		455		474		501
2015										47		137		215		305		371		395
2016												52		146		246		323		374
2017														66		175		313		381
2018																74		169		270
2019																		70		190
2020																				53
Total																				$	3,578

Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	287
Accident years 2011 - 2020 from tables above	1,837
All Accident years	$	2,124

This product line represents first party commercial product lines that are short-tailed in nature, such as property, inland marine, ocean marine, surety and A&H. There is a wide diversity of products, primary and excess coverages, and policy sizes. During this ten-year period, this product line was also impacted by natural catastrophes mainly in the 2012, 2017, and 2018 accident years.

Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	1,960	$	1,934		$	1,877	$	1,856	$	1,835	$	1,840	$	1,835	$	1,835	$	1,835	$	1,833	$	4	416
2012			2,033			1,916		1,883		1,864		1,859		1,847		1,844		1,850		1,844		(8)		426
2013						1,434		1,424		1,337		1,360		1,340		1,340		1,338		1,344		7		455
2014								1,643		1,661		1,579		1,559		1,549		1,550		1,558		10		483
2015										1,736		1,745		1,650		1,638		1,605		1,589		(1)		545
2016												1,911		1,890		1,799		1,782		1,818		32		650
2017														2,704		2,608		2,505		2,522		51		763
2018																2,053		2,240		2,175		71		901
2019																		2,052		2,037		166		1,036
2020																				3,150		1,061		927
Total																				$	19,870

Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	939	$	1,574		$	1,718	$	1,777	$	1,787	$	1,811	$	1,816	$	1,821	$	1,825	$	1,830
2012			715			1,577		1,698		1,767		1,795		1,822		1,816		1,842		1,844
2013						651		1,138		1,238		1,285		1,311		1,324		1,333		1,335
2014								820		1,374		1,484		1,506		1,532		1,546		1,554
2015										727		1,343		1,488		1,556		1,572		1,574
2016												846		1,504		1,656		1,733		1,761
2017														979		2,087		2,303		2,394
2018																1,027		1,825		2,018
2019																		1,030		1,677
2020																				1,396
Total																				$	17,383

Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	4
Accident years 2011 - 2020 from tables above	2,487
All Accident years	$	2,491

North America Personal P&C Insurance — Short-tail

Chubb provides personal lines coverages for high-net-worth individuals and families in North America including homeowners, automobile, valuable articles (including fine art), umbrella liability, and recreational marine insurance offered through independent regional agents and brokers. A portfolio acquired from Fireman’s Fund is presented on a prospective basis beginning in May of accident year 2015. Reserves associated with prior accident periods were acquired through a loss portfolio transfer, which does not allow for a retrospective presentation. During this ten-year period, this segment was also impacted by natural catastrophes, mainly in 2012, 2017 and 2018 accident years.

Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	2,208	$	2,210		$	2,185	$	2,173	$	2,164	$	2,161	$	2,160	$	2,158	$	2,159	$	2,157	$	7	179
2012			2,185			2,183		2,183		2,191		2,186		2,186		2,189		2,194		2,190		18		188
2013						1,860		1,888		1,897		1,900		1,924		1,937		1,945		1,948		26		132
2014								2,205		2,206		2,192		2,146		2,160		2,147		2,141		14		144
2015										2,494		2,550		2,561		2,544		2,563		2,570		21		148
2016												2,440		2,535		2,545		2,482		2,471		45		154
2017														3,035		3,069		3,002		2,998		96		163
2018																3,010		3,037		3,103		244		169
2019																		2,957		2,993		329		155
2020																				2,931		1,119		100
Total																				$	25,502

Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	1,360	$	1,835		$	1,972	$	2,052	$	2,105	$	2,129	$	2,139	$	2,146	$	2,148	$	2,149
2012			1,177			1,806		1,957		2,063		2,117		2,149		2,164		2,163		2,165
2013						1,043		1,504		1,688		1,787		1,843		1,885		1,895		1,917
2014								1,310		1,765		1,926		2,035		2,080		2,106		2,116
2015										1,499		2,084		2,271		2,392		2,478		2,508
2016												1,453		2,052		2,211		2,314		2,370
2017														1,698		2,520		2,668		2,799
2018																1,926		2,549		2,706
2019																		1,668		2,437
2020																				1,334
Total																				$	22,501

North America Personal P&C Insurance — Short-tail (continued)
Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	24
Accident years 2011 - 2020 from tables above	3,001
All Accident years	$	3,025

This product line is comprised of D&O liability, E&O liability, financial institutions (including crime/fidelity coverages), and non-U.S. general liability as well as aviation and political risk. Exposures are located around the world, including Europe, Latin America, and Asia. Approximately 45 percent of Chubb Overseas General business is generated by European accounts, exclusive of Lloyd's market. There is some U.S. exposure in Casualty from multinational accounts and in financial lines for Lloyd's market. The financial lines coverages are typically written on a claims-made form, while general liability coverages are typically on an occurrence basis and comprised of a mix of primary and excess businesses.

Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	1,255	$	1,262		$	1,254	$	1,244	$	1,158	$	1,090	$	1,079	$	1,027	$	1,023	$	1,025	$	31	37
2012			1,290			1,261		1,326		1,346		1,343		1,337		1,315		1,304		1,272		87		38
2013						1,281		1,279		1,276		1,322		1,276		1,242		1,182		1,148		86		39
2014								1,279		1,352		1,362		1,378		1,293		1,206		1,165		151		39
2015										1,196		1,296		1,328		1,351		1,326		1,265		199		41
2016												1,232		1,337		1,407		1,437		1,425		341		43
2017														1,227		1,332		1,381		1,433		384		43
2018																1,330		1,383		1,447		671		43
2019																		1,409		1,480		809		40
2020																				1,810		1,493		28
Total																				$	13,470

Overseas General Insurance — Casualty — Long-tail (continued)
Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	86	$	243		$	393	$	528	$	631	$	713	$	789	$	842	$	876	$	901
2012			75			252		441		597		713		857		929		973		1,040
2013						85		267		428		579		725		829		899		952
2014								111		293		473		608		725		811		876
2015										86		287		497		679		802		884
2016												127		324		534		687		815
2017														98		323		535		702
2018																112		334		503
2019																		126		341
2020																				110
Total																				$	7,124

Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	486
Accident years 2011 - 2020 from tables above	6,346
All Accident years	$	6,832

This product line is comprised of commercial fire, marine (predominantly cargo), surety, personal automobile (in Latin America, Asia Pacific and Japan), personal cell phones, personal residential (including high net worth), energy and construction. In general, these lines have relatively stable payment and reporting patterns although they are impacted by natural catastrophes mainly in the 2011, 2017, and 2018 accident years. Latin America and Europe each make up about 30 percent of the Chubb Overseas General non-casualty book.

Overseas General Insurance — Non-Casualty — Short-tail (continued)
Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves		Reported Claims (in thousands)
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	1,908	$	1,995		$	1,938	$	1,898	$	1,879	$	1,867	$	1,859	$	1,849	$	1,844	$	1,843	$	6	543
2012			1,712			1,702		1,661		1,605		1,599		1,590		1,575		1,570		1,562		13		555
2013						1,787		1,780		1,714		1,665		1,660		1,633		1,620		1,610		19		573
2014								1,863		1,932		1,875		1,864		1,828		1,817		1,810		7		548
2015										1,963		2,083		2,062		2,030		2,011		2,003		24		571
2016												2,070		2,071		2,058		2,036		2,040		22		581
2017														2,222		2,264		2,245		2,225		18		589
2018																2,186		2,276		2,237		48		624
2019																		2,208		2,228		94		640
2020																				2,571		804		518
Total																				$	20,129

Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	765	$	1,486		$	1,694	$	1,750	$	1,780	$	1,795	$	1,804	$	1,808	$	1,807	$	1,806
2012			679			1,237		1,425		1,485		1,508		1,518		1,530		1,532		1,532
2013						696		1,284		1,480		1,512		1,549		1,567		1,575		1,578
2014								758		1,438		1,651		1,715		1,746		1,759		1,774
2015										857		1,560		1,793		1,875		1,897		1,927
2016												1,013		1,679		1,881		1,954		1,981
2017														1,051		1,848		2,029		2,106
2018																1,006		1,753		1,962
2019																		1,050		1,747
2020																				1,085
Total																				$	17,498

(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	94
Accident years 2011 - 2020 from tables above	2,631
All Accident years	$	2,725

This product line includes proportional and excess coverages in general, automobile liability, professional liability, medical malpractice and workers' compensation, with exposures located around the world. In general, reinsurance exhibits less stable development patterns than primary business. In particular, general casualty reinsurance and excess coverages are long-tailed and can be very volatile.

Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	408	$	415		$	430	$	433	$	428	$	418	$	415	$	409	$	402	$	389	$	15
2012			387			384		392		395		379		373		372		374		379		11
2013						321		327		330		331		332		324		317		311		13
2014								334		335		340		343		345		348		331		16
2015										285		290		300		301		309		306		22
2016												224		228		236		236		245		27
2017														215		217		221		218		28
2018																246		249		256		48
2019																		239		248		90
2020																				247		153
Total																				$	2,930

Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	70	$	146		$	195	$	236	$	267	$	292	$	312	$	325	$	332	$	338
2012			78			168		223		262		293		309		324		336		342
2013						65		143		186		222		242		260		269		272
2014								92		185		218		249		265		277		287
2015										90		159		192		217		233		250
2016												58		113		143		159		175
2017														47		100		122		140
2018																42		96		126
2019																		40		90
2020																				41
Total																				$	2,061

Global Reinsurance — Casualty — Long-tail (continued)
Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	331
Accident years 2011 - 2020 from tables above	869
All Accident years	$	1,200

This product line includes property, property catastrophe, marine, credit/surety, A&H and energy. This product line is impacted by natural catastrophes, particularly in the 2011, 2017 and 2018 accident years. Of the non-catastrophe book, the mixture of business varies by year with approximately 77 percent of loss on proportional treaties in treaty year 2011 and after. This percentage has increased over time with the proportion being approximately 59 percent for treaty years 2011 to 2012 growing to an average of 82 percent for treaty years 2013 to 2020, with the remainder being written on an excess of loss basis.

Global Reinsurance — Non-Casualty — Short-tail (continued)
Net Incurred Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31						As of December 31 2020
(in millions of U.S. dollars)					Unaudited																	Net IBNR Reserves
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	277	$	279		$	276	$	266	$	267	$	268	$	267	$	268	$	267	$	269	$	1
2012			233			211		202		192		191		188		186		186		184		1
2013						162		160		148		143		144		141		141		140		—
2014								167		182		183		186		184		183		182		3
2015										147		155		162		162		155		161		4
2016												184		189		192		194		190		5
2017														397		424		454		451		10
2018																288		300		303		(8)
2019																		143		141		29
2020																				212		110
Total																				$	2,233

Global Reinsurance — Non-Casualty — Short-tail (continued)
Net Cumulative Paid Loss and Allocated Loss Adjustment Expenses
																Years Ended December 31
(in millions of U.S. dollars)					Unaudited
Accident Year	2011		2012			2013		2014		2015		2016		2017		2018		2019		2020
2011	$	87	$	179		$	210	$	236	$	254	$	259	$	262	$	263	$	264	$	265
2012			45			130		157		167		173		178		180		181		180
2013						46		103		121		131		134		137		137		139
2014								66		131		154		165		171		173		175
2015										56		104		133		143		147		153
2016												57		133		161		172		178
2017														191		322		402		415
2018																94		258		277
2019																		35		86
2020																				63
Total																				$	1,931

Net Liabilities for Loss and Allocated Loss Adjustment Expenses
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	10
Accident years 2011 - 2020 from tables above	302
All Accident years	$	312

Supplementary PPD [Table Text Block]

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	(94)
Accident years 2011 - 2020 from tables above	(256)
All Accident years	$	(350)

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	(176)
Accident years 2011 - 2020 from tables above	(117)
All Accident years	$	(293)

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	23
Accident years 2011 - 2020 from tables above	19
All Accident years	$	42

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	2
Accident years 2011 - 2020 from tables above	(37)
All Accident years	$	(35)

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	(1)
Accident years 2011 - 2020 from tables above	85
All Accident years	$	84

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	(59)
Accident years 2011 - 2020 from tables above	9
All Accident years	$	(50)

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	(8)
Accident years 2011 - 2020 from tables above	(69)
All Accident years	$	(77)

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	(10)
Accident years 2011 - 2020 from tables above	(12)
All Accident years	$	(22)

Supplementary Information: (Favorable)/ Adverse Prior Period Development
(in millions of U.S. dollars)	December 31, 2020
Accident years prior to 2011	$	—
Accident years 2011 - 2020 from tables above	(2)
All Accident years	$	(2)

Schedule of Historical Claims [Table Text Block]

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	10	%	16	%	10	%	7	%	5	%	4	%	3	%	2	%	2	%	1	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	5	%	14	%	17	%	16	%	12	%	7	%	5	%	3	%	2	%	1	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	12	%	23	%	19	%	14	%	10	%	5	%	3	%	2	%	1	%	—	%

North America Commercial P&C Insurance — Non-Casualty — Short-tail (continued)
Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	46	%	38	%	8	%	3	%	1	%	1	%	—	%	1	%	—	%	—	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	57	%	24	%	7	%	5	%	3	%	1	%	1	%	—	%	—	%	—	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	8	%	15	%	15	%	12	%	10	%	8	%	6	%	4	%	4	%	3	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	45	%	35	%	11	%	3	%	2	%	1	%	1	%	—	%	—	%	—	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	21	%	23	%	12	%	10	%	7	%	5	%	4	%	3	%	2	%	2	%

Supplementary Information: Average Annual Percentage Payout of Net Incurred Claims by Age, as of December 31, 2020 (Unaudited)
Age in Years	1		2		3		4		5		6		7		8		9		10
Percentage	33	%	38	%	14	%	6	%	4	%	2	%	1	%	1	%	—	%	—	%

Supplementary PPD Reconciliation [Table Text Block]

The following table presents a reconciliation of the loss development triangles above to prior period development:

	Components of PPD
Year Ended December 31, 2020 (in millions of U.S. dollars) (favorable)/unfavorable	2011 - 2019 accident years (implied PPD per loss triangles)		Accident years prior to 2011		Other (1)			PPD on loss reserves		RIPs, Expense adjustments, and earned premiums			Total
North America Commercial P&C Insurance
Long-tail	$	(354)	$	(247)	$	(102)		$	(703)	$	31		$	(672)
Short-tail	(37)		2		5			(30)		—			(30)
	(391)		(245)		(97)		(2)	(733)		31		(3)	(702)
North America Personal P&C Insurance (Short-tail)	85		(1)		(3)			81		(18)			63
Overseas General Insurance
Long-tail	9		(59)		1			(49)		—			(49)
Short-tail	(69)		(8)		(24)			(101)		—			(101)
	(60)		(67)		(23)		(4)	(150)		—			(150)
Global Reinsurance
Long-tail	(12)		(10)		(1)			(23)		(2)			(25)
Short-tail	(2)		—		(1)			(3)		(1)			(4)
	(14)		(10)		(2)			(26)		(3)			(29)
Subtotal	$	(380)	$	(323)	$	(125)		$	(828)	$	10		$	(818)
North America Agricultural Insurance (Short-tail)								$	(19)	$	9		$	(10)
Corporate (Long-tail)								433		—			433
Consolidated PPD								$	(414)	$	19		$	(395)

(1)        Other includes the impact of foreign exchange.

(2)     Includes favorable development of $80 million related to our Alternative Risk Solutions business (U.S. and Bermuda) and an adjustment to exclude $15 million in unfavorable development in the workers' compensation line, associated with an increase in exposure for which additional premiums were collected; the remaining difference relates to a number of other items, none of which are individually material.

(3)     Includes premium returns associated with our Alternative Risk Solutions business, which is excluded from the triangles.

(4)     Includes favorable development of $22 million related to International A&H business; the remaining difference relates to a number of other items, none of which are individually material.

Prior Period Development, by Segment [Table Text Block]

Years Ended December 31 (in millions of U.S. dollars, except for percentages)	Long-tail		Short-tail		Total		% of beginning net unpaid reserves (1)
2020
North America Commercial P&C Insurance	$	(672)	$	(30)	$	(702)	1.4	%
North America Personal P&C Insurance	—		63		63		0.1	%
North America Agricultural Insurance	—		(10)		(10)		—	%
Overseas General Insurance	(49)		(101)		(150)		0.3	%
Global Reinsurance	(25)		(4)		(29)		0.1	%
Corporate	433		—		433		0.9	%
Total	$	(313)	$	(82)	$	(395)	0.8	%
2019
North America Commercial P&C Insurance	$	(668)	$	19	$	(649)	1.3	%
North America Personal P&C Insurance	—		(95)		(95)		0.2	%
North America Agricultural Insurance	—		(80)		(80)		0.2	%
Overseas General Insurance	(68)		(24)		(92)		0.2	%
Global Reinsurance	(59)		30		(29)		0.1	%
Corporate	153		—		153		0.3	%
Total	$	(642)	$	(150)	$	(792)	1.6	%
2018
North America Commercial P&C Insurance	$	(395)	$	(215)	$	(610)	1.2	%
North America Personal P&C Insurance	—		41		41		0.1	%
North America Agricultural Insurance	—		(110)		(110)		0.2	%
Overseas General Insurance	(67)		(145)		(212)		0.4	%
Global Reinsurance	(69)		19		(50)		0.1	%
Corporate	45		—		45		0.1	%
Total	$	(486)	$	(410)	$	(896)	1.8	%

(1)     Calculated based on the beginning of period consolidated net unpaid losses and loss expenses.

Schedule Of Asbestos Environmental Loss Roll Forward and by segment

The following table presents a roll-forward of consolidated A&E loss reserves including allocated loss expense reserves for A&E exposures, and the valuation allowance for uncollectible paid and unpaid reinsurance recoverables:

	Asbestos				Environmental				Total
(in millions of U.S. dollars)	Gross		Net		Gross		Net		Gross		Net
Balance at December 31, 2017	$	1,621	$	1,051	$	607	$	476	$	2,228	$	1,527
Incurred activity	136		75		101		(97)		237		(22)		(1)
Paid activity	(265)		(162)		(83)		104		(348)		(58)
Balance at December 31, 2018	1,492		964		625		483		2,117		1,447
Incurred activity	129		70		46		28		175		98		(1)
Paid activity	(162)		(118)		(142)		(101)		(304)		(219)
Balance at December 31, 2019	1,459		916		529		410		1,988		1,326
Incurred activity	150		90		79		41		229		131		(1)
Paid activity	(258)		(133)		(91)		(72)		(349)		(205)
Balance at December 31, 2020	$	1,351	$	873	$	517	$	379	$	1,868	$	1,252

(1)     Excludes unallocated loss expenses and the net activity reflects third-party reinsurance other than the aggregate excess of loss reinsurance provided by National Indemnity Company (NICO) to Westchester Specialty (see Westchester Specialty section below).

The A&E net loss reserves including allocated loss expense reserves and valuation allowance for uncollectible reinsurance at December 31, 2020 and 2019 shown in the table above is comprised of:

	December 31
(in millions of U.S. dollars)	2020		2019
Brandywine operations	$	736	$	754
Westchester Specialty	103		117
Chubb Corp	333		381
Other, mainly Overseas General Insurance	80		74
Total	$	1,252	$	1,326