Willis Towers Watson Public Limited (WTW) 10-Q 29 Apr 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 26, 2021
Cover [Abstract]
Amendment Flag	false
Document Type	10-Q
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	WILLIS TOWERS WATSON PLC
Entity Central Index Key	0001140536
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		128,976,752
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Trading Symbol	WLTW
Title of 12(b) Security	Ordinary Shares, nominal value $0.000304635 per share
Security Exchange Name	NASDAQ
Entity File Number	001-16503
Entity Incorporation, State or Country Code	L2
Entity Tax Identification Number	98-0352587
Entity Address, Address Line One	c/o Willis Group Limited
Entity Address, Address Line Two	51 Lime Street
Entity Address, City or Town	London
Entity Address, Country	GB
Entity Address, Postal Zip Code	EC3M 7DQ
City Area Code	011
Local Phone Number	44-20-3124-6000
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenue	$ 2,590	$ 2,466
Costs of providing services
Salaries and benefits	1,523	1,394
Other operating expenses	417	484
Depreciation	71	98
Amortization	103	121
Transaction and integration expenses	24	9
Total costs of providing services	2,138	2,106
Income from operations	452	360
Interest expense	(59)	(61)
Other income, net	439	92
INCOME FROM OPERATIONS BEFORE INCOME TAXES	832	391
Provision for income taxes	(96)	(78)
NET INCOME	736	313
Income attributable to non-controlling interests	(3)	(8)
NET INCOME ATTRIBUTABLE TO WILLIS TOWERS WATSON	$ 733	$ 305
EARNINGS PER SHARE
Basic earnings per share	$ 5.64	$ 2.36
Diluted earnings per share	$ 5.63	$ 2.34
Comprehensive income before non-controlling interests	$ 786	$ 93
Comprehensive income attributable to non-controlling interests	(5)	(7)
Comprehensive income attributable to Willis Towers Watson	$ 781	$ 86

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
ASSETS
Cash and cash equivalents	$ 1,960	$ 2,089
Fiduciary assets	15,911	15,160
Accounts receivable, net	2,569	2,555
Prepaid and other current assets	432	497
Total current assets	20,872	20,301
Fixed assets, net	951	1,014
Goodwill	10,986	11,204
Other intangible assets, net	2,878	3,043
Right-of-use assets	841	902
Pension benefits assets	991	971
Other non-current assets	1,113	1,096
Total non-current assets	17,760	18,230
TOTAL ASSETS	38,632	38,531
LIABILITIES AND EQUITY
Fiduciary liabilities	15,911	15,160
Deferred revenue and accrued expenses	1,526	2,161
Current debt	471	971
Current lease liabilities	147	152
Other current liabilities	965	888
Total current liabilities	19,020	19,332
Long-term debt	4,632	4,664
Liability for pension benefits	1,278	1,405
Deferred tax liabilities	576	561
Provision for liabilities	390	407
Long-term lease liabilities	857	918
Other non-current liabilities	305	312
Total non-current liabilities	8,038	8,267
TOTAL LIABILITIES	27,058	27,599
COMMITMENTS AND CONTINGENCIES	0	0
EQUITY
Additional paid-in capital	10,765	10,748
Retained earnings	3,075	2,434
Accumulated other comprehensive loss, net of tax	(2,311)	(2,359)
Treasury shares, at cost, 17,519 shares in 2021 and 2020	(3)	(3)
Total Willis Towers Watson shareholders’ equity	11,526	10,820
Non-controlling interests	48	112
Total equity	11,574	10,932
TOTAL LIABILITIES AND EQUITY	$ 38,632	$ 38,531

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Preference shares, nominal value (USD per share)	$ 0.000115	$ 0.000115
Preference shares, shares authorized	1,000,000,000	1,000,000,000
Preference shares, shares issued	0	0
Ordinary shares, $0.000304635 nominal value [Member]
Ordinary shares, nominal value	$ 0.000304635	$ 0.000304635
Ordinary shares, shares authorized	1,510,003,775	1,510,003,775
Ordinary shares, shares issued	128,974,389	128,964,579
Ordinary shares, shares outstanding	128,974,389	128,964,579
Treasury shares	17,519	17,519

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS (USED IN)/FROM OPERATING ACTIVITIES
NET INCOME		$ 736	$ 313
Adjustments to reconcile net income to total net cash from operating activities:
Depreciation		71	98
Amortization		103	121
Non-cash lease expense		37	34
Net periodic benefit of defined benefit pension plans		(42)	(46)
Provision for doubtful receivables from clients		8	24
Provision for/(benefit from) deferred income taxes		10	(23)
Share-based compensation		27	(1)
Net gain on disposal of operations		(359)	0
Non-cash foreign exchange gain		(2)	(12)
Other, net		(24)	23
Changes in operating assets and liabilities, net of effects from purchase of subsidiaries:
Accounts receivable		(115)	(46)
Fiduciary assets		(1,784)	(2,873)
Fiduciary liabilities		1,784	2,873
Other assets		(15)	7
Other liabilities		(556)	(482)
Provisions		(7)	13
Net cash (used in)/from operating activities		(128)	23
CASH FLOWS FROM/(USED IN) INVESTING ACTIVITIES
Additions to fixed assets and software for internal use		(37)	(66)
Capitalized software costs		(14)	(15)
Acquisitions of operations, net of cash acquired		0	(66)
Net proceeds from sale of operations		696	0
Other, net		0	(15)
Net cash from/(used in) investing activities		645	(162)
CASH FLOWS (USED IN)/FROM FINANCING ACTIVITIES
Net borrowings on revolving credit facility		0	396
Repayments of debt		(508)	(128)
Proceeds from issuance of shares		1	3
Payments of deferred and contingent consideration related to acquisitions		(17)	0
Dividends paid		(92)	(84)
Acquisitions of and dividends paid to non-controlling interests		(17)	(1)
Net cash (used in)/from financing activities		(633)	186
(DECREASE)/INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH		(116)	47
Effect of exchange rate changes on cash, cash equivalents and restricted cash		(14)	(36)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF PERIOD	[1]	2,096	895
CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF PERIOD	[1]	$ 1,966	$ 906
[1]	As a result of the acquired TRANZACT collateralized facility, cash, cash equivalents and restricted cash included $6 million and $7 million of restricted cash at March 31, 2021 and December 31, 2020, respectively, which is included within prepaid and other current assets on our condensed consolidated balance sheets. There was $8 million of restricted cash held at March 31, 2020 and December 31, 2019.

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Restricted cash	$ 6	$ 7
Prepaid Expenses and Other Current Assets [Member] | Tranzact Collateralized Facility [Member]
Restricted cash	$ 6	$ 7

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions		Total	Shares outstanding [Member]	Ordinary shares and APIC [Member]	Retained earnings [Member]	Treasury shares [Member]	AOCL [Member]	[1]	Total WTW shareholders' equity [Member]	Non-controlling interests [Member]
Equity, beginning balance at Dec. 31, 2019		$ 10,369		$ 10,687	$ 1,792	$ (3)	$ (2,227)		$ 10,249	$ 120
Equity, beginning balance (in shares) at Dec. 31, 2019			128,690
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		313			305				305	8
Dividends declared		(88)			(88)				(88)
Dividends attributable to non-controlling interests		(1)								(1)
Other comprehensive (loss) gain		(220)					(219)		(219)	(1)
Issuance of shares under employee stock compensation plans		3		3					3
Issuance of shares under employee stock compensation plans (in shares)			36
Share-based compensation and net settlements		9		9					9
Foreign currency translation		4		4					4
Equity, ending balance at Mar. 31, 2020		10,389		10,703	2,009	(3)	(2,446)		10,263	126
Equity, ending balance (in shares) at Mar. 31, 2020			128,726
Equity, beginning balance at Dec. 31, 2020		10,932		10,748	2,434	(3)	(2,359)		10,820	112
Equity, beginning balance (in shares) at Dec. 31, 2020			128,965
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		736			733				733	3
Dividends declared		(92)			(92)				(92)
Dividends attributable to non-controlling interests		(17)								(17)
Other comprehensive (loss) gain		50					48		48	2
Issuance of shares under employee stock compensation plans		1		1					1
Issuance of shares under employee stock compensation plans (in shares)			9
Share-based compensation and net settlements		12		12					12
Reduction of non-controlling interests	[2]	(52)								(52)
Foreign currency translation		4		4					4
Equity, ending balance at Mar. 31, 2021		$ 11,574		$ 10,765	$ 3,075	$ (3)	$ (2,311)		$ 11,526	$ 48
Equity, ending balance (in shares) at Mar. 31, 2021			128,974
[1]	Accumulated other comprehensive loss, net of tax (‘AOCL’).
[2]	Attributable to the divestiture of our less than wholly-owned Miller subsidiary.

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Changes in Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Stockholders Equity [Abstract]
Dividends declared per share	$ 0.71	$ 0.68

Nature of Operations

Nature of Operations	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Operations	Note 1 — Nature of Operations Willis Towers Watson plc is a leading global advisory, broking and solutions company that helps clients around the world turn risk into a path for growth. The Company has more than 46,000 employees and services clients in more than 140 countries. We design and deliver solutions that manage risk, optimize benefits, cultivate talent, and expand the power of capital to protect and strengthen institutions and individuals. Our risk management services include strategic risk consulting (including providing actuarial analysis), a variety of due diligence services, the provision of practical on-site risk control services (such as health and safety and property loss control consulting), and analytical and advisory services (such as hazard modeling and reinsurance optimization studies). We also assist our clients with planning for addressing incidents or crises when they occur. These services include contingency planning, security audits and product tampering plans. We help our clients enhance business performance by delivering consulting services, technology and solutions that optimize benefits and cultivate talent. Our services and solutions encompass such areas as employee benefits, total rewards, talent and benefits outsourcing. In addition, we provide investment advice to help our clients develop disciplined and efficient strategies to meet their investment goals and expand the power of capital. As an insurance broker, we act as an intermediary between our clients and insurance carriers by advising on their risk management requirements, helping them to determine the best means of managing risk and negotiating and placing insurance with insurance carriers through our global distribution network. We operate a private Medicare marketplace in the U.S. through which, along with our active employee marketplace, we help our clients move to a more sustainable economic model by capping and controlling the costs associated with healthcare benefits. We also provide direct-to-consumer sales of Medicare coverage. We are not an insurance company, and therefore we do not underwrite insurable risks for our own account. We believe our broad perspective allows us to see the critical intersections between talent, assets and ideas - the dynamic formula that drives business performance. Proposed Combination with Aon plc On March 9, 2020, WTW and Aon plc (‘Aon’) issued an announcement disclosing that the respective boards of directors of WTW and Aon had reached agreement on the terms of a recommended acquisition of WTW by Aon. Under the terms of the agreement each WTW shareholder will receive 1.08 Aon ordinary shares for each WTW ordinary share. At the time of the announcement, it was estimated that upon completion of the combination, existing Aon shareholders will own approximately 63% and existing WTW shareholders will own approximately 37% of the combined company on a fully diluted basis. The transaction was approved by the shareholders of both WTW and Aon during meetings of the respective shareholders held on August 26, 2020 and remains subject to other customary closing conditions, including required regulatory approvals. The antitrust regulatory review of the transaction remains ongoing. In addition, there are numerous other regulatory approvals and other closing conditions that need to be met. The parties expect the transaction to close by the end of the first half of 2021, subject to satisfaction of these conditions.

Basis of Presentation and Recen

Basis of Presentation and Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Recent Accounting Pronouncements	Note 2 Basis of Presentation The accompanying unaudited quarterly condensed consolidated financial statements of Willis Towers Watson and our subsidiaries are presented in accordance with the rules and regulations of the SEC for quarterly reports on Form 10-Q and therefore do not include all of the information and footnotes required by U.S. GAAP. In the opinion of management, these condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments, which are necessary for a fair presentation of the condensed consolidated financial statements and results for the interim periods. All intercompany accounts and transactions have been eliminated in consolidation. The condensed consolidated financial statements should be read together with the Company’s Annual Report on Form 10-K, filed with the SEC on February 23, 2021, and may be accessed via EDGAR on the SEC’s web site at www.sec.gov. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results that can be expected for the entire year. The Company experiences seasonal fluctuations of its revenue. Revenue is typically higher during the Company’s first and fourth quarters due primarily to the timing of broking-related activities. The results reflect certain estimates and assumptions made by management, including those estimates used in calculating acquisition consideration and fair value of tangible and intangible assets and liabilities, professional liability claims, estimated bonuses, valuation of billed and unbilled receivables, and anticipated tax liabilities that affect the amounts reported in the condensed consolidated financial statements and related notes. Risks and Uncertainties Related to the COVID-19 Pandemic The COVID-19 pandemic has had an adverse impact on global commercial activity, including the global supply chain, and has contributed to significant volatility in the global financial markets including, among other effects, occasional declines in the equity markets, changes in interest rates and reduced liquidity on a global basis. With regard to the effects on our own business operations and those of our clients, suppliers and other third parties with whom we interact, the Company has regularly considered the impact of COVID-19 on our business, taking into account our business resilience and continuity plans, financial modeling and stress testing of liquidity and financial resources. Generally, the COVID-19 pandemic did not have a material adverse impact on our overall financial results during 2020 or on our results for the first quarter of 2021; however, during 2020 and through the first quarter of 2021, the COVID-19 pandemic continues to negatively impact our revenue growth, primarily in our businesses that are discretionary in nature. We believe such level of impact will continue through much of 2021, at least until a sufficient portion of the populations in jurisdictions where we do business have been vaccinated and social-distancing orders are lessened or lifted. As part of the significant estimates and assumptions that are inherent in our financial statements, we have considered the impact COVID-19 will have on our client behavior and the economic environment looking forward for the remainder of 2021 and throughout the geographies in which we operate. These estimates and assumptions include the collectability of billed and unbilled receivables, the estimation of revenue, and the fair value of our reporting units, tangible and intangible assets and contingent consideration. With regard to collectability of receivables, we believe we may continue to face atypical delays in client payments going forward. The demand for certain discretionary lines of business has decreased, and we believe that decrease may continue to impact our financial results in succeeding periods. Non-discretionary lines of business have also been, to some extent, adversely affected and may be adversely affected in the future. Further, reduced economic activity or disruption in insurance markets could reduce the demand for or the extent of insurance coverage. For example, we have seen instances where the reduced demand for air travel has reduced the extent of insurance coverage needed. Also, the increased frequency and severity of coverage disputes between our clients and (re)insurers arising out of the pandemic could increase our professional liability risk. We will continue to monitor the situation and assess any implications to our business and our stakeholders. The extent to which COVID-19 impacts our business and financial position will depend on future developments, which are difficult to predict. These future developments may include the severity and scope of the COVID-19 outbreak, which may unexpectedly change or worsen, and the types and duration of measures imposed by governmental authorities to contain the virus or address its impact. We continue to expect that the COVID-19 pandemic will negatively impact our revenue and operating results in fiscal 2021. We believe that these trends and uncertainties are similar to those faced by other comparable registrants as a result of the pandemic. Recent Accounting Pronouncements Adopted In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes

Divestitures

Divestitures	3 Months Ended
	Mar. 31, 2021
Dispositions [Abstract]
Divestitures	Note 3 Miller Divestiture On March 1, 2021, the Company completed the transaction to sell its U.K.-based, majority-owned wholesale subsidiary Miller for final total consideration of GBP 623 million ($818 million), which includes amounts paid to the minority shareholder. The $356 million net tax-exempt gain on the sale was included in Other income, net in the condensed consolidated statement of comprehensive income during the three months ended March 31, 2021. Prior to disposal, Miller was included within the Investment, Risk and Reinsurance segment. Max Matthiessen Divestiture In September 2020, the Company completed the transaction to sell its Swedish majority-owned subsidiary MM Holding AB (‘Max Matthiessen’) for total consideration of SEK 2.3 billion ($262 million) plus certain other adjustments, resulting in a tax-exempt gain on the sale of $86 million, which was included in Other income, net in the consolidated statement of comprehensive income during the year ended December 31, 2020. Of the total consideration, the Company financed a SEK 600 million ($ 68 million) note repayable by the purchaser. The note has no fixed term but is repayable subject to certain terms and conditions and bears an interest rate that could range from 5 % to 10 %, increasing the longer the note remains outstanding. This note receivable is included in Other non-current assets in the condensed consolidated balance sheet. Prior to disposal, Max Matthiessen was included within the Investment, Risk and Reinsurance segment .

Revenue

Revenue	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
Revenue	Note 4 Disaggregation of Revenue The Company reports revenue by segment in Note 5 — Three Months Ended March 31, HCB CRB IRR BDA Corporate ( i ) Total 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Broking $ 97 $ 83 $ 717 $ 648 $ 412 $ 433 $ 152 $ 98 $ — $ — $ 1,378 $ 1,262 Consulting 594 582 44 47 123 93 — — 2 2 763 724 Outsourced administration 132 128 25 25 4 3 132 133 — — 293 289 Other 49 47 4 1 65 83 — — 1 1 119 132 Total revenue by service offering 872 840 790 721 604 612 284 231 3 3 2,553 2,407 Reimbursable expenses and other ( i ) 11 15 — — 1 3 2 3 (5 ) 6 9 27 Total revenue from customer contracts $ 883 $ 855 $ 790 $ 721 $ 605 $ 615 $ 286 $ 234 $ (2 ) $ 9 $ 2,562 $ 2,434 Interest and other income (ii) 3 10 20 18 1 3 3 — 1 1 28 32 Total revenue $ 886 $ 865 $ 810 $ 739 $ 606 $ 618 $ 289 $ 234 $ (1 ) $ 10 $ 2,590 $ 2,466 ______________ ( i ) Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the condensed consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations and impacts from hedged revenue transactions. ( i i ) Interest and other income is included in segment revenue and total revenue, however it has been presented separately in the above tables because it does not arise directly from contracts with customers. Individual revenue streams aggregating to approximately 5% of total revenue from customer contracts for the three months ended March 31, 2021 and 2020 have been included within the Other line in the tables above. The following table presents revenue by the geography where our work is performed for the three months ended March 31, 2021 and 2020. The reconciliation to total revenue on our condensed consolidated statement of comprehensive income and to segment revenue is shown in the table above. Three Months Ended March 31, HCB CRB IRR BDA Corporate Total 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 North America $ 468 $ 476 $ 247 $ 233 $ 186 $ 170 $ 282 $ 229 $ 2 $ 2 $ 1,185 $ 1,110 Great Britain 147 126 155 137 311 321 — — — — 613 584 Western Europe 171 156 261 244 59 76 — — 1 1 492 477 International 86 82 127 107 48 45 2 2 — — 263 236 Total revenue by geography $ 872 $ 840 $ 790 $ 721 $ 604 $ 612 $ 284 $ 231 $ 3 $ 3 $ 2,553 $ 2,407 Contract Balances The Company reports accounts receivable, net on the condensed consolidated balance sheet, which includes billed and unbilled receivables and current contract assets. In addition to accounts receivable, net, the Company had the following non-current contract assets and deferred revenue balances at March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Billed receivables, net of allowance for doubtful accounts of $44 million and $41 million $ 1,727 $ 1,697 Unbilled receivables 508 445 Current contract assets 334 413 Accounts receivable, net $ 2,569 $ 2,555 Non-current accounts receivable, net $ 22 $ 34 Non-current contract assets $ 380 $ 329 Deferred revenue $ 620 $ 549 During the three months ended March 31, 2021, revenue of approximately $275 million was recognized that was reflected as deferred revenue at December 31, 2020. During the three months ended March 31, 2021, the Company recognized revenue of approximately $23 million related to performance obligations satisfied in a prior period. Performance Obligations The Company has contracts for which performance obligations have not been satisfied as of March 31, 2021 or have been partially satisfied as of this date. The following table shows the expected timing for the satisfaction of the remaining performance obligations. This table does not include contract renewals or variable consideration, which was excluded from the transaction prices in accordance with the guidance on constraining estimates of variable consideration. In addition, in accordance with ASC 606, Revenue From Contracts With Customers • Performance obligations which are part of a contract that has an original expected duration of less than one year, and • Performance obligations satisfied in accordance with ASC 606-10-55-18 (‘right to invoice’). Remainder of 2021 2022 2023 onward Total Revenue expected to be recognized on contracts as of March 31, 2021 $ 429 $ 426 $ 476 $ 1,331 Since most of the Company’s contracts are cancellable with less than one year’s notice, and have no substantive penalty for cancellation, the majority of the Company’s remaining performance obligations as of March 31, 2021 have been excluded from the table above.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segment Information	Note 5 Willis Towers Watson has four reportable operating segments or business areas: • Human Capital and Benefits (‘HCB’) • Corporate Risk and Broking (‘CRB’) • Investment, Risk and Reinsurance (‘IRR’) • Benefits Delivery and Administration (‘BDA’) Willis Towers Watson’s chief operating decision maker is its chief executive officer. We determined that the operational data used by the chief operating decision maker is at the segment level. Management bases strategic goals and decisions on these segments and the data presented below is used to assess the adequacy of strategic decisions and the methods of achieving these strategies and related financial results. Management evaluates the performance of its segments and allocates resources to them based on net operating income on a pre-tax basis. The Company experiences seasonal fluctuations of its revenue. Revenue is typically higher during the Company’s first and fourth quarters due primarily to the timing of broking-related activities. The following table presents segment revenue and segment operating income for our reportable segments for the three months ended March 31, 2021 and 2020. Three Months Ended March 31, HCB CRB IRR BDA Total 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Segment revenue $ 875 $ 850 $ 810 $ 739 $ 605 $ 615 $ 287 $ 231 $ 2,577 $ 2,435 Segment operating income/(loss) $ 220 $ 213 $ 162 $ 127 $ 290 $ 277 $ 7 $ (11 ) $ 679 $ 606 The following table presents a reconciliation of the information reported by segment to the Company’s condensed consolidated statement of comprehensive income amounts reported for the three months ended March 31, 2021 and 2020. Three Months Ended March 31, 2021 2020 Revenue: Total segment revenue $ 2,577 $ 2,435 Reimbursable expenses and other 13 31 Revenue $ 2,590 $ 2,466 Total segment operating income $ 679 $ 606 Amortization (103 ) (121 ) Transaction and integration expenses ( i ) (24 ) (9 ) Unallocated, net (ii) (100 ) (116 ) Income from operations 452 360 Interest expense (59 ) (61 ) Other income, net 439 92 Income from operations before income taxes $ 832 $ 391 ( i ) Includes mainly transaction costs related to the proposed Aon combination. (ii) Includes certain costs, primarily related to corporate functions which are not directly related to the segments, and certain differences between budgeted expenses determined at the beginning of the year and actual expenses that we report for U.S. GAAP purposes. The Company does not currently provide asset information by reportable segment as it does not routinely evaluate the total asset position by segment.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Note 6 — Income Taxes Provision for income taxes for the three months ended March 31, 2021 was $96 million compared to $78 million for the three months ended March 31, 2020. The effective tax rate was 11.5% for the three months ended March 31, 2021 and 20.0% for the three months ended March 31, 2020. These effective tax rates are calculated using extended values from our condensed consolidated statements of comprehensive income and are therefore more precise tax rates than can be calculated from rounded values. The current quarter effective tax rate was lower primarily due to the tax-exempt disposal of our Miller business. The Company recognizes deferred tax balances related to the undistributed earnings of subsidiaries when it expects that it will recover those undistributed earnings in a taxable manner, such as through receipt of dividends or sale of the investments. Historically, we have not provided taxes on cumulative earnings of our subsidiaries that have been reinvested indefinitely. As a result of our plans to restructure or distribute accumulated earnings of certain foreign operations, we have recorded an estimate of foreign withholding and state income taxes. However, we assert that the historical cumulative earnings of our other subsidiaries are reinvested indefinitely, and therefore do not provide deferred tax liabilities on these amounts. The Company records valuation allowances against net deferred tax assets based on whether it is more likely than not that the deferred tax assets will be realized. We have liabilities for uncertain tax positions under ASC 740 of $49 million, excluding interest and penalties. The Company believes the outcomes that are reasonably possible within the next 12 months may result in a reduction in the liability for uncertain tax positions of approximately $4 million to $8 million, excluding interest and penalties.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Note 7 The components of goodwill are outlined below for the three months ended March 31, 2021: HCB CRB IRR BDA Total Balance at December 31, 2020: Goodwill, gross $ 4,346 $ 2,378 $ 1,694 $ 3,278 $ 11,696 Accumulated impairment losses (130 ) (362 ) — — (492 ) Goodwill, net - December 31, 2020 4,216 2,016 1,694 3,278 11,204 Goodwill disposals — — (188 ) — (188 ) Foreign exchange (17 ) (16 ) 3 — (30 ) Balance at March 31, 2021: Goodwill, gross 4,329 2,362 1,509 3,278 11,478 Accumulated impairment losses (130 ) (362 ) — — (492 ) Goodwill, net - March 31, 2021 $ 4,199 $ 2,000 $ 1,509 $ 3,278 $ 10,986 Other Intangible Assets The following table reflects changes in the net carrying amounts of the components of finite-lived intangible assets for the three months ended March 31, 2021: Client relationships Software Trademark and trade name Other Total Balance at December 31, 2020: Intangible assets, gross $ 4,065 $ 761 $ 1,054 $ 108 $ 5,988 Accumulated amortization (2,031 ) (659 ) (220 ) (35 ) (2,945 ) Intangible assets, net - December 31, 2020 2,034 102 834 73 3,043 Intangible asset disposals (46 ) — (8 ) — (54 ) Amortization (69 ) (19 ) (11 ) (4 ) (103 ) Foreign exchange (10 ) — — 2 (8 ) Balance at March 31, 2021: Intangible assets, gross 3,865 759 1,040 110 5,774 Accumulated amortization (1,956 ) (676 ) (225 ) (39 ) (2,896 ) Intangible assets, net - March 31, 2021 $ 1,909 $ 83 $ 815 $ 71 $ 2,878 The weighted-average remaining life of amortizable intangible assets at March 31, 2021 was 13.4 years. The table below reflects the future estimated amortization expense for amortizable intangible assets for the remainder of 2021 and for subsequent years: Amortization Remainder of 2021 $ 268 2022 308 2023 257 2024 224 2025 205 Thereafter 1,616 Total $ 2,878

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2021
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Note 8 We are exposed to certain foreign currency risks. Where possible, we identify exposures in our business that can be offset internally. Where no natural offset is identified, we may choose to enter into various derivative transactions. These instruments have the effect of reducing our exposure to unfavorable changes in foreign currency rates. The Company’s board of directors reviews and approves policies for managing this risk as summarized below. Additional information regarding our derivative financial instruments can be found in Note 10 — Fair Value Measurements and Note 16 — Accumulated Other Comprehensive Loss. Foreign Currency Risk Certain non-U.S. subsidiaries receive revenue and incur expenses in currencies other than their functional currency, and as a result, the foreign subsidiary’s functional currency revenue and/or expenses will fluctuate as the currency rates change. Additionally, the forecasted Pounds sterling expenses of our London brokerage market operations may exceed their Pounds sterling revenue, and the entity with such operations may also hold significant foreign currency asset or liability positions in the condensed consolidated balance sheet. To reduce such variability, we use foreign exchange contracts to hedge against this currency risk. These derivatives were designated as hedging instruments and at March 31, 2021 and December 31, 2020 had total notional amounts of $249 million and $340 million, respectively, and had net fair value assets of $8 million and $5 million, respectively. As part of and prior to our disposal of Miller (see Note 3 – Divestitures), and prior to their contract expiration, we closed derivatives designated as hedging instruments with notional values of $27 million that were outstanding at December 31, 2020. At March 31, 2021, the Company estimates, based on current exchange rates, there will be $6 million of net derivative gains on forward exchange rates reclassified from accumulated other comprehensive loss into earnings within the next twelve months as the forecast transactions affect earnings. At March 31, 2021, our longest outstanding maturity was 1.7 years. The effects of the material derivative instruments that are designated as hedging instruments on the condensed consolidated statements of comprehensive income for the three months ended March 31, 2021 and 2020 are below. Amounts pertaining to the ineffective portion of hedging instruments and those excluded from effectiveness testing were immaterial for the three months ended March 31, 2021 and 2020. Three Months Ended March 31, Gain/(loss) recognized in OCI (effective element) 2021 2020 Forward exchange contracts $ 4 $ (24 ) Location of (loss)/gain reclassified from Accumulated OCL into income (effective element) (Loss)/gain reclassified from Accumulated OCL into income (effective element) 2021 2020 Revenue $ (2 ) $ — Salaries and benefits 3 (2 ) $ 1 $ (2 ) We also enter into foreign currency transactions, primarily to hedge certain intercompany loans and other balance sheet exposures in currencies other than the functional currency of a given entity. These derivatives are not generally designated as hedging instruments and at both March 31, 2021 and December 31, 2020, we had notional amounts of $1.5 billion. At March 31, 2021 and December 31, 2020, we had a net fair value liability of $1 million and a net fair value asset of $15 million, respectively. The effects of derivatives that have not been designated as hedging instruments on the condensed consolidated statements of comprehensive income for the three months ended March 31, 2021 and 2020 are as follows: Loss recognized in income Three Months Ended March 31, Derivatives not designated as hedging instruments: Location of loss recognized in income 2021 2020 Forward exchange contracts Other income, net $ (16 ) $ (12 )

Debt

Debt	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt	Note 9 Current debt consists of the following: March 31, 2021 December 31, 2020 Revolving $1.25 billion credit facility ( i ) $ — $ — 5.750% senior notes due 2021 — 500 3.500% senior notes due 2021 450 449 Current portion of collateralized facility 21 22 $ 471 $ 971 Long-term debt consists of the following: March 31, 2021 December 31, 2020 Revolving $1.25 billion credit facility $ — $ — Collateralized facility (ii) 27 33 2.125% senior notes due 2022 (iii) 633 659 4.625% senior notes due 2023 249 249 3.600% senior notes due 2024 647 647 4.400% senior notes due 2026 546 546 4.500% senior notes due 2028 596 596 2.950% senior notes due 2029 726 726 6.125% senior notes due 2043 271 271 5.050% senior notes due 2048 395 395 3.875% senior notes due 2049 542 542 $ 4,632 $ 4,664 ( i ) The $1.25 billion revolving credit facility expires on March 7, 2022. (ii) At March 31, 2021 and December 31, 2020, the Company had $92 million and $98 million, respectively, of renewal commissions receivables pledged as collateral for this facility (ii i ) Notes issued in Euro (€540 million). Payment of 5.750% Senior Notes due 2021 In March 2021, the $500 million 5.750% senior notes matured. The principal and interest were repaid by the Company using cash on-hand. At March 31, 2021 and December 31, 2020, we were in compliance with all financial covenants.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 10 The Company has categorized its assets and liabilities that are measured at fair value on a recurring and non-recurring basis into a three-level fair value hierarchy, based on the reliability of the inputs used to determine fair value as follows: • Level 1: refers to fair values determined based on quoted market prices in active markets for identical assets; • Level 2: refers to fair values estimated using observable market-based inputs or unobservable inputs that are corroborated by market data; and • Level 3: includes fair values estimated using unobservable inputs that are not corroborated by market data. The following methods and assumptions were used by the Company in estimating its fair value disclosure for financial instruments: • Available-for-sale securities are classified as Level 1 because we use quoted market prices in determining the fair value of these securities. • Market values for our derivative instruments have been used to determine the fair value of forward foreign exchange contracts based on estimated amounts the Company would receive or have to pay to terminate the agreements, taking into account observable information about the current foreign currency forward rates. Such financial instruments are classified as Level 2 in the fair value hierarchy. • Contingent consideration payable is classified as Level 3, and we estimate fair value based on the likelihood and timing of achieving the relevant milestones of each arrangement, applying a probability assessment to each of the potential outcomes, which at times includes the use of a Monte Carlo simulation, and discounting the probability-weighted payout. Typically, milestones are based on revenue or earnings growth for the acquired business. The following tables present our assets and liabilities measured at fair value on a recurring basis at March 31, 2021 and December 31, 2020: Fair Value Measurements on a Recurring Basis at March 31, 2021 Balance Sheet Location Level 1 Level 2 Level 3 Total Assets: Available-for-sale securities: Mutual funds / exchange traded funds Prepaid and other current assets and other non-current assets $ 9 $ — $ — $ 9 Derivatives: Derivative financial instruments ( i ) Prepaid and other current assets and other non-current assets $ — $ 10 $ — $ 10 Liabilities: Contingent consideration: Contingent consideration (ii) Other current liabilities and other non-current liabilities $ — $ — $ 28 $ 28 Derivatives: Derivative financial instruments ( i ) Other current liabilities and other non-current liabilities $ — $ 3 $ — $ 3 Fair Value Measurements on a Recurring Basis at December 31, 2020 Balance Sheet Location Level 1 Level 2 Level 3 Total Assets: Available-for-sale securities: Mutual funds / exchange traded funds Prepaid and other current assets and other non-current assets $ 8 $ — $ — $ 8 Derivatives: Derivative financial instruments ( i ) Prepaid and other current assets and other non-current assets $ — $ 27 $ — $ 27 Liabilities: Contingent consideration: Contingent consideration (ii) Other current liabilities and other non-current liabilities $ — $ — $ 45 $ 45 Derivatives: Derivative financial instruments ( i ) Other current liabilities and other non-current liabilities $ — $ 7 $ — $ 7 ( i ) See Note 8 — Derivative Financial Instruments for further information on our derivative investments. (ii) Probability weightings are based on our knowledge of the past and planned performance of the acquired entity to which the contingent consideration applies. The fair value weighted-average discount rates used on our material contingent consideration calculations were 10.92% and 9.46% at March 31, 2021 and December 31, 2020, respectively. The range of these discount rates was 3.53% - 13.00% at March 31, 2021. Using different probability weightings and discount rates could result in an increase or decrease of the contingent consideration payable. The following table summarizes the change in fair value of the Level 3 liabilities: Fair Value Measurements Using Significant Unobservable Inputs (Level 3) March 31, 2021 Balance at December 31, 2020 $ 45 Payments (17 ) Balance at March 31, 2021 $ 28 There were no significant transfers to or from Level 3 in the three months ended March 31, 2021. Fair value information about financial instruments not measured at fair value The following tables present our liabilities not measured at fair value on a recurring basis at March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Carrying Value Fair Value Carrying Value Fair Value Assets: Long-term note receivable $ 67 $ 69 $ 71 $ 73 Liabilities: Current debt $ 471 $ 476 $ 971 $ 985 Long-term debt $ 4,632 $ 5,141 $ 4,664 $ 5,488 The carrying values of our revolving credit facility and collateralized facility approximate their fair values. The fair values above, which exclude accrued interest, are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or ability to dispose of the financial instruments. The fair values of our respective senior notes and long-term note receivable are considered Level 2 financial instruments as they are corroborated by observable market data.

Retirement Benefits

Retirement Benefits	3 Months Ended
	Mar. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Retirement Benefits	Note 11 Defined Benefit Plans and Post-retirement Welfare Plans Willis Towers Watson sponsors both qualified and non-qualified defined benefit pension plans and other post-retirement welfare (‘PRW’) plans throughout the world. The majority of our plan assets and obligations are in the U.S. and the U.K. We have also included disclosures related to defined benefit plans in certain other countries, including Canada, France, Germany and Ireland. Together, these disclosed funded and unfunded plans represent 99% of Willis Towers Watson’s pension and PRW obligations and are disclosed herein. Components of Net Periodic Benefit (Income)/Cost for Defined Benefit Pension and Post-retirement Welfare Plans The following table sets forth the components of net periodic benefit (income)/cost for the Company’s defined benefit pension and PRW plans for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 U.S. U.K. Other PRW U.S. U.K. Other PRW Service cost $ 20 $ 4 $ 6 $ — $ 18 $ 4 $ 5 $ — Interest cost 23 14 3 — 33 18 4 1 Expected return on plan assets (77 ) (43 ) (9 ) — (73 ) (62 ) (8 ) — Settlement 1 — — — — — — — Amortization of net loss 11 7 1 — 9 6 — — Amortization of prior service credit — (4 ) — (1 ) — (4 ) — (1 ) Net periodic benefit (income)/cost $ (22 ) $ (22 ) $ 1 $ (1 ) $ (13 ) $ (38 ) $ 1 $ — Employer Contributions to Defined Benefit Pension Plans The Company made $60 million of contributions to its U.S. plans for the three months ended March 31, 2021 and does not anticipate making any additional contributions over the remainder of the fiscal year. The Company made contributions of $10 million to its U.K. plans for the three months ended March 31, 2021 and anticipates making additional contributions of $31 million for the remainder of the fiscal year. The Company made contributions of $16 million to its other plans for the three months ended March 31, 2021 and anticipates making additional contributions of $9 million for the remainder of the fiscal year. Defined Contribution Plans The Company made contributions to its defined contribution plans of $43 million during both the three months ended March 31, 2021 and 2020.

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Note 12 The following table presents lease costs recorded on our condensed consolidated statements of comprehensive income for the three months ended March 31, 2021 and 2020, respectively: Three Months Ended March 31, 2021 2020 Finance lease cost: Amortization of right-of-use assets $ — $ 1 Interest on lease liabilities 1 1 Operating lease cost 46 47 Variable lease cost 13 10 Sublease income (5 ) (5 ) Total lease cost, net $ 55 $ 54 The total lease cost is recognized in different locations in our condensed consolidated statements of comprehensive income. Amortization of the finance lease ROU assets is included in depreciation, while the interest cost component of these finance leases is included in interest expense. All other costs are included in other operating expenses.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 13 Indemnification Agreements Willis Towers Watson has various agreements which provide that it may be obligated to indemnify the other party to the agreement with respect to certain matters. Generally, these indemnification provisions are included in contracts arising in the normal course of business and in connection with the purchase and sale of certain businesses. It is not possible to predict the maximum potential amount of future payments that may become due under these indemnification agreements because of the conditional nature of the Company’s obligations and the unique facts of each particular agreement. However, we do not believe that any potential liability that may arise from such indemnity provisions is probable or material. Legal Proceedings In the ordinary course of business, the Company is subject to various actual and potential claims, lawsuits and other proceedings. Some of the claims, lawsuits and other proceedings seek damages in amounts which could, if assessed, be significant. We expect the impact of claims or demands not described below to be immaterial to the Company’s condensed consolidated financial statements. The Company also receives subpoenas in the ordinary course of business and, from time to time, receives requests for information in connection with governmental investigations. Errors and omissions claims, lawsuits, and other proceedings arising in the ordinary course of business are covered in part by professional indemnity or other appropriate insurance. The terms of this insurance vary by policy year. Regarding self-insured risks, the Company has established provisions which are believed to be adequate in light of current information and legal advice, or, in certain cases, where a range of loss exists, the Company accrues the minimum amount in the range if no amount within the range is a better estimate than any other amount. The Company adjusts such provisions from time to time according to developments. See Note 14 — On the basis of current information, the Company does not expect that the actual claims, lawsuits and other proceedings to which it is subject, or potential claims, lawsuits, and other proceedings relating to matters of which it is aware, will ultimately have a material adverse effect on its financial condition, results of operations or liquidity. Nonetheless, given the large or indeterminate amounts sought in certain of these actions, and the inherent unpredictability of litigation and disputes with insurance companies, it is possible that an adverse outcome or settlement in certain matters could, from time to time, have a material adverse effect on the Company’s results of operations or cash flows in particular quarterly or annual periods. In addition, given the early stages of some litigation or regulatory proceedings described below, it may not be possible to predict their outcomes or resolutions, and it is possible that any one or more of these events may have a material adverse effect on the Company. The Company provides for contingent liabilities based on ASC 450, Contingencies, Willis Towers Watson Merger-Related Securities Litigation The Company was named as a defendant in two consolidated actions arising out of the 2016 ‘merger of equals’ between Towers Watson and Willis (the ‘Merger’), consisting of a consolidated shareholder class action pending in the United States District Court for the Eastern District of Virginia, captioned ‘In re Willis Towers Watson plc Proxy Litigation,’ Master File No. 1:17-cv-1338-AJT-JFA (the ‘Federal Action’), and a consolidated putative shareholder class action pending in the Delaware Court of Chancery, captioned ‘In re Towers Watson & Co. Stockholders Litigation,’ C.A. No. 2018-0132-KSJM (the ‘Delaware Action’). The complaints in these actions generally allege that the defendants omitted material information from the proxy disclosures relating to the Merger, including with respect to potential conflicts of interest, and, as a result, that Towers Watson’s stockholders approved the Merger based on inadequate information. Based on these allegations, among others, the complaint in the Federal Action asserts claims under Sections 14(a) and 20(a) of the Securities Exchange Act of 1934, and the complaint in the Delaware Action asserts claims under Delaware state law for breach of fiduciary duty and aiding and abetting breach of fiduciary duty. On or about November 19, 2020, the parties to the Federal Action and the Delaware Action reached an agreement in principle to resolve the Federal Action and the Delaware Action for $75 million and $15 million, respectively. The Company agreed to the settlement and the payment of the settlement amounts to eliminate the distraction, burden, expense and uncertainty of further litigation. Further, in reaching the settlement, the parties understood and agreed that there is no admission of liability or wrongdoing by the Company or any of the other defendants in either the Federal Action or the Delaware Action. The Company and the other defendants expressly deny any liability or wrongdoing with respect to the matters alleged in the Federal Action and the Delaware Action. On January 15, 2021, the parties to the Federal Action and the Delaware Action signed formal stipulations of settlement, which memorialized the terms of the agreement in principle, and which the plaintiffs in the Federal Action and the Delaware Action then filed with each of the respective courts. Also on January 15, 2021, the plaintiff in the Federal Action filed a motion to preliminarily approve the settlement. On January 21, 2021, the court in the Federal Action preliminarily approved the settlement, approved the form of notice to be disseminated to class members, and scheduled a final fairness hearing on the settlement for May 21, 2021. On January 25, 2021, the court in the Delaware Action approved the form of notice to be disseminated to class members and scheduled a final fairness hearing on the settlement for May 25, 2021. The settlement is contingent upon final approval by the courts in both the Federal Action and the Delaware Action. The Company made the $ 90 million aggregate settlement payment in escrow in February 2021, but it will not be distributed to class members unless and until the settlement is finally approved by the courts in both the Federal Action and the Delaware Action and not subject to any further appeal. During 2020, the Company recognized $65 million of expense, net of $25 million of insurance and other recoveries. Additional insurance recoveries are possible. Aviation Broking Competition Investigations In October 2017, the European Commission (‘Commission’) disclosed to us that it has initiated civil investigation proceedings in respect of a suspected infringement of E.U. competition rules involving several broking firms, including our principal U.K. broking subsidiary and one of its parent entities. In particular, the Commission has stated that the civil proceedings concern the exchange of commercially sensitive information between competitors in relation to aviation and aerospace insurance and reinsurance broking products and services in the European Economic Area, as well as possible coordination between competitors. In November 2020, the Commission advised us that it has decided to close the proceedings against us without taking further action. Since 2017, we have become aware that other countries are conducting their own investigations of the same or similar alleged conduct relating to certain competition rules involving several of our broking firms in certain countries, including, without limitation, Brazil. In January 2019, the Brazil Conselho Administrativo de Defesa Economica (‘CADE’) launched an administrative proceeding to investigate alleged sharing of competitive and commercially sensitive information in the insurance and reinsurance brokerage industry for aviation and aerospace and related ancillary services. The CADE identified 11 entities under investigation, including Willis Group Limited, one of our U.K. subsidiaries. While the investigation is currently ongoing, we do not expect our liability, if any, to be material.

Supplementary Information for C

Supplementary Information for Certain Balance Sheet Accounts	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Supplementary Information for Certain Balance Sheet Accounts	Note 14 — Supplementary Information for Certain Balance Sheet Accounts Additional details of specific balance sheet accounts are detailed below. Prepaid and other current assets consist of the following: March 31, 2021 December 31, 2020 Prepayments and accrued income $ 138 $ 124 Deferred contract costs 74 108 Derivatives and investments 26 42 Deferred compensation plan assets 13 14 Retention incentives 7 3 Corporate income and other taxes 99 83 Insurance and other recovery receivables 2 25 Restricted cash 6 7 Acquired renewal commissions receivable 14 16 Other current assets 53 75 Total prepaid and other current assets $ 432 $ 497 Deferred revenue and accrued expenses consist of the following: March 31, 2021 December 31, 2020 Accounts payable, accrued liabilities and deferred income $ 913 $ 862 Accrued discretionary and incentive compensation 383 851 Litigation settlements — 210 Accrued vacation 182 161 Other employee-related liabilities 48 77 Total deferred revenue and accrued expenses $ 1,526 $ 2,161 Provision for liabilities consists of the following: March 31, 2021 December 31, 2020 Claims, lawsuits and other proceedings $ 316 $ 325 Other provisions 74 82 Total provision for liabilities $ 390 $ 407

Other Income, Net

Other Income, Net	3 Months Ended
	Mar. 31, 2021
Other Income And Expenses [Abstract]
Other Income, Net	Note 15 — Other Income, Net Other income, net consists of the following: Three Months Ended March 31, 2021 2020 Gain on disposal of operations $ 359 $ — Net periodic pension and postretirement benefit credits 76 76 Interest in earnings of associates and other investments 2 2 Foreign exchange gain 2 12 Other — 2 Other income, net $ 439 $ 92

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Accumulated Other Comprehensive Loss	Note 16 — Accumulated Other Comprehensive Loss Changes in accumulated other comprehensive loss, net of non-controlling interests, and net of tax are provided in the following tables for the three months ended March 31, 2021 and 2020. These tables exclude amounts attributable to non-controlling interests, which are not material for further disclosure. Foreign currency translation (i) Derivative instruments (i) Defined pension and post-retirement benefit costs (ii) Total 2021 2020 2021 2020 2021 2020 2021 2020 Balance at December 31, 2020 and 2019, respectively $ (400 ) $ (538 ) $ 9 $ 13 $ (1,968 ) $ (1,702 ) $ (2,359 ) $ (2,227 ) Other comprehensive income/(loss) before reclassifications (42 ) (208 ) 7 (19 ) 1 (4 ) (34 ) (231 ) Loss/(gain) reclassified from accumulated other comprehensive loss (net of income tax benefit of $6 and $0, respectively) (iii) 44 — (1 ) 1 39 11 82 12 Net current-period other comprehensive income/(loss) 2 (208 ) 6 (18 ) 40 7 48 (219 ) Balance at March 31, 2021 and 2020, respectively $ (398 ) $ (746 ) $ 15 $ (5 ) $ (1,928 ) $ (1,695 ) $ (2,311 ) $ (2,446 ) (i) Reclassification adjustments from accumulated other comprehensive loss related to derivative instruments are included in Revenue and Salaries and benefits in the accompanying condensed consolidated statements of comprehensive income. See Note 8 — Derivative Financial Instruments for additional details regarding the reclassification adjustments for the derivative settlements. (ii) Reclassification adjustments from accumulated other comprehensive loss are included in the computation of net periodic pension cost (see Note 11 — Retirement Benefits). These components are included in Other income, net in the accompanying condensed consolidated statements of comprehensive income. (iii) Includes reclassifications of $44 million and $31 million of foreign currency translation and defined pension and post-retirement benefit costs, respectively, attributable to the gain on disposal of our Miller business (see Note 3 — Divestitures). The net gain on disposal is included in Other income, net in the accompanying condensed consolidated statements of comprehensive income.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings Per Share	Note 17 — Earnings Per Share Basic and diluted earnings per share are calculated by dividing net income attributable to Willis Towers Watson by the average number of ordinary shares outstanding during each period. The computation of diluted earnings per share reflects the potential dilution that could occur if dilutive securities and other contracts to issue shares were exercised or converted into shares or resulted in the issuance of shares that then shared in the net income of the Company. At March 31, 2021 and 2020, there were 0.1 million and 0.2 million time-based share options, and 0.5 million and 0.3 million restricted performance-based stock units outstanding, respectively. There were 0.3 million performance-based options at both March 31, 2021 and 2020. The Company’s restricted time-based stock units were immaterial at March 31, 2021 and 2020. Basic and diluted earnings per share are as follows: Three Months Ended March 31, 2021 2020 Net income attributable to Willis Towers Watson $ 733 $ 305 Basic average number of shares outstanding 130 130 Dilutive effect of potentially issuable shares — — Diluted average number of shares outstanding 130 130 Basic earnings per share $ 5.64 $ 2.36 Dilutive effect of potentially issuable shares (0.01 ) (0.02 ) Diluted earnings per share $ 5.63 $ 2.34 For the three months ended March 31, 2021, 0.2 million restricted stock units were not included in the computation of the dilutive effect of potentially issuable shares because their effect was anti-dilutive; there were no anti-dilutive restricted stock units for the three months ended March 31, 2020. There were no anti-dilutive options for the three months ended March 31, 2021 and 2020.

Basis of Presentation and Rec_2

Basis of Presentation and Recent Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited quarterly condensed consolidated financial statements of Willis Towers Watson and our subsidiaries are presented in accordance with the rules and regulations of the SEC for quarterly reports on Form 10-Q and therefore do not include all of the information and footnotes required by U.S. GAAP. In the opinion of management, these condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments, which are necessary for a fair presentation of the condensed consolidated financial statements and results for the interim periods. All intercompany accounts and transactions have been eliminated in consolidation. The condensed consolidated financial statements should be read together with the Company’s Annual Report on Form 10-K, filed with the SEC on February 23, 2021, and may be accessed via EDGAR on the SEC’s web site at www.sec.gov. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results that can be expected for the entire year. The Company experiences seasonal fluctuations of its revenue. Revenue is typically higher during the Company’s first and fourth quarters due primarily to the timing of broking-related activities. The results reflect certain estimates and assumptions made by management, including those estimates used in calculating acquisition consideration and fair value of tangible and intangible assets and liabilities, professional liability claims, estimated bonuses, valuation of billed and unbilled receivables, and anticipated tax liabilities that affect the amounts reported in the condensed consolidated financial statements and related notes.
Risks and Uncertainties Related to the COVID-19 Pandemic	Risks and Uncertainties Related to the COVID-19 Pandemic The COVID-19 pandemic has had an adverse impact on global commercial activity, including the global supply chain, and has contributed to significant volatility in the global financial markets including, among other effects, occasional declines in the equity markets, changes in interest rates and reduced liquidity on a global basis. With regard to the effects on our own business operations and those of our clients, suppliers and other third parties with whom we interact, the Company has regularly considered the impact of COVID-19 on our business, taking into account our business resilience and continuity plans, financial modeling and stress testing of liquidity and financial resources. Generally, the COVID-19 pandemic did not have a material adverse impact on our overall financial results during 2020 or on our results for the first quarter of 2021; however, during 2020 and through the first quarter of 2021, the COVID-19 pandemic continues to negatively impact our revenue growth, primarily in our businesses that are discretionary in nature. We believe such level of impact will continue through much of 2021, at least until a sufficient portion of the populations in jurisdictions where we do business have been vaccinated and social-distancing orders are lessened or lifted. As part of the significant estimates and assumptions that are inherent in our financial statements, we have considered the impact COVID-19 will have on our client behavior and the economic environment looking forward for the remainder of 2021 and throughout the geographies in which we operate. These estimates and assumptions include the collectability of billed and unbilled receivables, the estimation of revenue, and the fair value of our reporting units, tangible and intangible assets and contingent consideration. With regard to collectability of receivables, we believe we may continue to face atypical delays in client payments going forward. The demand for certain discretionary lines of business has decreased, and we believe that decrease may continue to impact our financial results in succeeding periods. Non-discretionary lines of business have also been, to some extent, adversely affected and may be adversely affected in the future. Further, reduced economic activity or disruption in insurance markets could reduce the demand for or the extent of insurance coverage. For example, we have seen instances where the reduced demand for air travel has reduced the extent of insurance coverage needed. Also, the increased frequency and severity of coverage disputes between our clients and (re)insurers arising out of the pandemic could increase our professional liability risk. We will continue to monitor the situation and assess any implications to our business and our stakeholders. The extent to which COVID-19 impacts our business and financial position will depend on future developments, which are difficult to predict. These future developments may include the severity and scope of the COVID-19 outbreak, which may unexpectedly change or worsen, and the types and duration of measures imposed by governmental authorities to contain the virus or address its impact. We continue to expect that the COVID-19 pandemic will negatively impact our revenue and operating results in fiscal 2021. We believe that these trends and uncertainties are similar to those faced by other comparable registrants as a result of the pandemic.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes
Fair Value of Financial Instruments	The Company has categorized its assets and liabilities that are measured at fair value on a recurring and non-recurring basis into a three-level fair value hierarchy, based on the reliability of the inputs used to determine fair value as follows: • Level 1: refers to fair values determined based on quoted market prices in active markets for identical assets; • Level 2: refers to fair values estimated using observable market-based inputs or unobservable inputs that are corroborated by market data; and • Level 3: includes fair values estimated using unobservable inputs that are not corroborated by market data. The following methods and assumptions were used by the Company in estimating its fair value disclosure for financial instruments: • Available-for-sale securities are classified as Level 1 because we use quoted market prices in determining the fair value of these securities. • Market values for our derivative instruments have been used to determine the fair value of forward foreign exchange contracts based on estimated amounts the Company would receive or have to pay to terminate the agreements, taking into account observable information about the current foreign currency forward rates. Such financial instruments are classified as Level 2 in the fair value hierarchy. • Contingent consideration payable is classified as Level 3, and we estimate fair value based on the likelihood and timing of achieving the relevant milestones of each arrangement, applying a probability assessment to each of the potential outcomes, which at times includes the use of a Monte Carlo simulation, and discounting the probability-weighted payout. Typically, milestones are based on revenue or earnings growth for the acquired business.

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
Disaggregation of Revenue	The following table presents revenue by service offering and segment, as well as a reconciliation to total revenue for the three months ended March 31, 2021 and 2020. Along with reimbursable expenses and other, total revenue by service offering represents our revenue from customer contracts. Three Months Ended March 31, HCB CRB IRR BDA Corporate ( i ) Total 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Broking $ 97 $ 83 $ 717 $ 648 $ 412 $ 433 $ 152 $ 98 $ — $ — $ 1,378 $ 1,262 Consulting 594 582 44 47 123 93 — — 2 2 763 724 Outsourced administration 132 128 25 25 4 3 132 133 — — 293 289 Other 49 47 4 1 65 83 — — 1 1 119 132 Total revenue by service offering 872 840 790 721 604 612 284 231 3 3 2,553 2,407 Reimbursable expenses and other ( i ) 11 15 — — 1 3 2 3 (5 ) 6 9 27 Total revenue from customer contracts $ 883 $ 855 $ 790 $ 721 $ 605 $ 615 $ 286 $ 234 $ (2 ) $ 9 $ 2,562 $ 2,434 Interest and other income (ii) 3 10 20 18 1 3 3 — 1 1 28 32 Total revenue $ 886 $ 865 $ 810 $ 739 $ 606 $ 618 $ 289 $ 234 $ (1 ) $ 10 $ 2,590 $ 2,466 ______________ ( i ) Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the condensed consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations and impacts from hedged revenue transactions. ( i i ) Interest and other income is included in segment revenue and total revenue, however it has been presented separately in the above tables because it does not arise directly from contracts with customers. Individual revenue streams aggregating to approximately 5% of total revenue from customer contracts for the three months ended March 31, 2021 and 2020 have been included within the Other line in the tables above. The following table presents revenue by the geography where our work is performed for the three months ended March 31, 2021 and 2020. The reconciliation to total revenue on our condensed consolidated statement of comprehensive income and to segment revenue is shown in the table above. Three Months Ended March 31, HCB CRB IRR BDA Corporate Total 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 North America $ 468 $ 476 $ 247 $ 233 $ 186 $ 170 $ 282 $ 229 $ 2 $ 2 $ 1,185 $ 1,110 Great Britain 147 126 155 137 311 321 — — — — 613 584 Western Europe 171 156 261 244 59 76 — — 1 1 492 477 International 86 82 127 107 48 45 2 2 — — 263 236 Total revenue by geography $ 872 $ 840 $ 790 $ 721 $ 604 $ 612 $ 284 $ 231 $ 3 $ 3 $ 2,553 $ 2,407
Contract with Customer, Asset and Liability	The Company reports accounts receivable, net on the condensed consolidated balance sheet, which includes billed and unbilled receivables and current contract assets. In addition to accounts receivable, net, the Company had the following non-current contract assets and deferred revenue balances at March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Billed receivables, net of allowance for doubtful accounts of $44 million and $41 million $ 1,727 $ 1,697 Unbilled receivables 508 445 Current contract assets 334 413 Accounts receivable, net $ 2,569 $ 2,555 Non-current accounts receivable, net $ 22 $ 34 Non-current contract assets $ 380 $ 329 Deferred revenue $ 620 $ 549
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction	In addition, in accordance with ASC 606, Revenue From Contracts With Customers • Performance obligations which are part of a contract that has an original expected duration of less than one year, and • Performance obligations satisfied in accordance with ASC 606-10-55-18 (‘right to invoice’). Remainder of 2021 2022 2023 onward Total Revenue expected to be recognized on contracts as of March 31, 2021 $ 429 $ 426 $ 476 $ 1,331

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following table presents segment revenue and segment operating income for our reportable segments for the three months ended March 31, 2021 and 2020. Three Months Ended March 31, HCB CRB IRR BDA Total 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Segment revenue $ 875 $ 850 $ 810 $ 739 $ 605 $ 615 $ 287 $ 231 $ 2,577 $ 2,435 Segment operating income/(loss) $ 220 $ 213 $ 162 $ 127 $ 290 $ 277 $ 7 $ (11 ) $ 679 $ 606
Net Operating Income of the Reported Segments	The following table presents a reconciliation of the information reported by segment to the Company’s condensed consolidated statement of comprehensive income amounts reported for the three months ended March 31, 2021 and 2020. Three Months Ended March 31, 2021 2020 Revenue: Total segment revenue $ 2,577 $ 2,435 Reimbursable expenses and other 13 31 Revenue $ 2,590 $ 2,466 Total segment operating income $ 679 $ 606 Amortization (103 ) (121 ) Transaction and integration expenses ( i ) (24 ) (9 ) Unallocated, net (ii) (100 ) (116 ) Income from operations 452 360 Interest expense (59 ) (61 ) Other income, net 439 92 Income from operations before income taxes $ 832 $ 391 ( i ) Includes mainly transaction costs related to the proposed Aon combination. (ii) Includes certain costs, primarily related to corporate functions which are not directly related to the segments, and certain differences between budgeted expenses determined at the beginning of the year and actual expenses that we report for U.S. GAAP purposes.

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Components of Goodwill	The components of goodwill are outlined below for the three months ended March 31, 2021: HCB CRB IRR BDA Total Balance at December 31, 2020: Goodwill, gross $ 4,346 $ 2,378 $ 1,694 $ 3,278 $ 11,696 Accumulated impairment losses (130 ) (362 ) — — (492 ) Goodwill, net - December 31, 2020 4,216 2,016 1,694 3,278 11,204 Goodwill disposals — — (188 ) — (188 ) Foreign exchange (17 ) (16 ) 3 — (30 ) Balance at March 31, 2021: Goodwill, gross 4,329 2,362 1,509 3,278 11,478 Accumulated impairment losses (130 ) (362 ) — — (492 ) Goodwill, net - March 31, 2021 $ 4,199 $ 2,000 $ 1,509 $ 3,278 $ 10,986
Changes in the Net Carrying Amount of the Components of Finite-Lived Intangible Assets	The following table reflects changes in the net carrying amounts of the components of finite-lived intangible assets for the three months ended March 31, 2021: Client relationships Software Trademark and trade name Other Total Balance at December 31, 2020: Intangible assets, gross $ 4,065 $ 761 $ 1,054 $ 108 $ 5,988 Accumulated amortization (2,031 ) (659 ) (220 ) (35 ) (2,945 ) Intangible assets, net - December 31, 2020 2,034 102 834 73 3,043 Intangible asset disposals (46 ) — (8 ) — (54 ) Amortization (69 ) (19 ) (11 ) (4 ) (103 ) Foreign exchange (10 ) — — 2 (8 ) Balance at March 31, 2021: Intangible assets, gross 3,865 759 1,040 110 5,774 Accumulated amortization (1,956 ) (676 ) (225 ) (39 ) (2,896 ) Intangible assets, net - March 31, 2021 $ 1,909 $ 83 $ 815 $ 71 $ 2,878
Schedule of Future Estimated Amortization Expense for Amortizable Intangible Assets	The table below reflects the future estimated amortization expense for amortizable intangible assets for the remainder of 2021 and for subsequent years: Amortization Remainder of 2021 $ 268 2022 308 2023 257 2024 224 2025 205 Thereafter 1,616 Total $ 2,878

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Designated [Member]
Schedule of Derivative Instruments Designated/Nondesignated As Hedging Instrument Effect on Condensed Consolidated Statements of Comprehensive Income	The effects of the material derivative instruments that are designated as hedging instruments on the condensed consolidated statements of comprehensive income for the three months ended March 31, 2021 and 2020 are below Three Months Ended March 31, Gain/(loss) recognized in OCI (effective element) 2021 2020 Forward exchange contracts $ 4 $ (24 ) Location of (loss)/gain reclassified from Accumulated OCL into income (effective element) (Loss)/gain reclassified from Accumulated OCL into income (effective element) 2021 2020 Revenue $ (2 ) $ — Salaries and benefits 3 (2 ) $ 1 $ (2 )
Nondesignated [Member]
Schedule of Derivative Instruments Designated/Nondesignated As Hedging Instrument Effect on Condensed Consolidated Statements of Comprehensive Income	The effects of derivatives that have not been designated as hedging instruments on the condensed consolidated statements of comprehensive income for the three months ended March 31, 2021 and 2020 are as follows: Loss recognized in income Three Months Ended March 31, Derivatives not designated as hedging instruments: Location of loss recognized in income 2021 2020 Forward exchange contracts Other income, net $ (16 ) $ (12 )

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Current and Long-term Debt	Current debt consists of the following: March 31, 2021 December 31, 2020 Revolving $1.25 billion credit facility ( i ) $ — $ — 5.750% senior notes due 2021 — 500 3.500% senior notes due 2021 450 449 Current portion of collateralized facility 21 22 $ 471 $ 971 Long-term debt consists of the following: March 31, 2021 December 31, 2020 Revolving $1.25 billion credit facility $ — $ — Collateralized facility (ii) 27 33 2.125% senior notes due 2022 (iii) 633 659 4.625% senior notes due 2023 249 249 3.600% senior notes due 2024 647 647 4.400% senior notes due 2026 546 546 4.500% senior notes due 2028 596 596 2.950% senior notes due 2029 726 726 6.125% senior notes due 2043 271 271 5.050% senior notes due 2048 395 395 3.875% senior notes due 2049 542 542 $ 4,632 $ 4,664 ( i ) The $1.25 billion revolving credit facility expires on March 7, 2022. (ii) At March 31, 2021 and December 31, 2020, the Company had $92 million and $98 million, respectively, of renewal commissions receivables pledged as collateral for this facility (ii i ) Notes issued in Euro (€540 million).

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present our assets and liabilities measured at fair value on a recurring basis at March 31, 2021 and December 31, 2020: Fair Value Measurements on a Recurring Basis at March 31, 2021 Balance Sheet Location Level 1 Level 2 Level 3 Total Assets: Available-for-sale securities: Mutual funds / exchange traded funds Prepaid and other current assets and other non-current assets $ 9 $ — $ — $ 9 Derivatives: Derivative financial instruments ( i ) Prepaid and other current assets and other non-current assets $ — $ 10 $ — $ 10 Liabilities: Contingent consideration: Contingent consideration (ii) Other current liabilities and other non-current liabilities $ — $ — $ 28 $ 28 Derivatives: Derivative financial instruments ( i ) Other current liabilities and other non-current liabilities $ — $ 3 $ — $ 3 Fair Value Measurements on a Recurring Basis at December 31, 2020 Balance Sheet Location Level 1 Level 2 Level 3 Total Assets: Available-for-sale securities: Mutual funds / exchange traded funds Prepaid and other current assets and other non-current assets $ 8 $ — $ — $ 8 Derivatives: Derivative financial instruments ( i ) Prepaid and other current assets and other non-current assets $ — $ 27 $ — $ 27 Liabilities: Contingent consideration: Contingent consideration (ii) Other current liabilities and other non-current liabilities $ — $ — $ 45 $ 45 Derivatives: Derivative financial instruments ( i ) Other current liabilities and other non-current liabilities $ — $ 7 $ — $ 7 ( i ) See Note 8 — Derivative Financial Instruments for further information on our derivative investments. (ii) Probability weightings are based on our knowledge of the past and planned performance of the acquired entity to which the contingent consideration applies. The fair value weighted-average discount rates used on our material contingent consideration calculations were 10.92% and 9.46% at March 31, 2021 and December 31, 2020, respectively. The range of these discount rates was 3.53% - 13.00% at March 31, 2021. Using different probability weightings and discount rates could result in an increase or decrease of the contingent consideration payable.
Schedule of Change in Fair Value of Level 3 Liabilities	The following table summarizes the change in fair value of the Level 3 liabilities: Fair Value Measurements Using Significant Unobservable Inputs (Level 3) March 31, 2021 Balance at December 31, 2020 $ 45 Payments (17 ) Balance at March 31, 2021 $ 28
Schedule of Liabilities Whose Carrying Values Differ From the Fair Value and are Not Measured on a Recurring Basis	Fair value information about financial instruments not measured at fair value The following tables present our liabilities not measured at fair value on a recurring basis at March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Carrying Value Fair Value Carrying Value Fair Value Assets: Long-term note receivable $ 67 $ 69 $ 71 $ 73 Liabilities: Current debt $ 471 $ 476 $ 971 $ 985 Long-term debt $ 4,632 $ 5,141 $ 4,664 $ 5,488

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Schedule of Net Periodic Benefit Cost	The following table sets forth the components of net periodic benefit (income)/cost for the Company’s defined benefit pension and PRW plans for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 U.S. U.K. Other PRW U.S. U.K. Other PRW Service cost $ 20 $ 4 $ 6 $ — $ 18 $ 4 $ 5 $ — Interest cost 23 14 3 — 33 18 4 1 Expected return on plan assets (77 ) (43 ) (9 ) — (73 ) (62 ) (8 ) — Settlement 1 — — — — — — — Amortization of net loss 11 7 1 — 9 6 — — Amortization of prior service credit — (4 ) — (1 ) — (4 ) — (1 ) Net periodic benefit (income)/cost $ (22 ) $ (22 ) $ 1 $ (1 ) $ (13 ) $ (38 ) $ 1 $ —

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Schedule of Lease Costs Recorded in Condensed Consolidated Statements of Comprehensive Income	The following table presents lease costs recorded on our condensed consolidated statements of comprehensive income for the three months ended March 31, 2021 and 2020, respectively: Three Months Ended March 31, 2021 2020 Finance lease cost: Amortization of right-of-use assets $ — $ 1 Interest on lease liabilities 1 1 Operating lease cost 46 47 Variable lease cost 13 10 Sublease income (5 ) (5 ) Total lease cost, net $ 55 $ 54

Supplementary Information for_2

Supplementary Information for Certain Balance Sheet Accounts (Tables)	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Prepaid and Other Current Assets	Prepaid and other current assets consist of the following: March 31, 2021 December 31, 2020 Prepayments and accrued income $ 138 $ 124 Deferred contract costs 74 108 Derivatives and investments 26 42 Deferred compensation plan assets 13 14 Retention incentives 7 3 Corporate income and other taxes 99 83 Insurance and other recovery receivables 2 25 Restricted cash 6 7 Acquired renewal commissions receivable 14 16 Other current assets 53 75 Total prepaid and other current assets $ 432 $ 497
Deferred Revenue and Accrued Expenses	Deferred revenue and accrued expenses consist of the following: March 31, 2021 December 31, 2020 Accounts payable, accrued liabilities and deferred income $ 913 $ 862 Accrued discretionary and incentive compensation 383 851 Litigation settlements — 210 Accrued vacation 182 161 Other employee-related liabilities 48 77 Total deferred revenue and accrued expenses $ 1,526 $ 2,161
Provisions for Liabilities	Provision for liabilities consists of the following: March 31, 2021 December 31, 2020 Claims, lawsuits and other proceedings $ 316 $ 325 Other provisions 74 82 Total provision for liabilities $ 390 $ 407

Other Income, Net (Tables)

Other Income, Net (Tables)	3 Months Ended
	Mar. 31, 2021
Other Income And Expenses [Abstract]
Schedule of Other Nonoperating Income	Other income, net consists of the following: Three Months Ended March 31, 2021 2020 Gain on disposal of operations $ 359 $ — Net periodic pension and postretirement benefit credits 76 76 Interest in earnings of associates and other investments 2 2 Foreign exchange gain 2 12 Other — 2 Other income, net $ 439 $ 92

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	Changes in accumulated other comprehensive loss, net of non-controlling interests, and net of tax are provided in the following tables for the three months ended March 31, 2021 and 2020. These tables exclude amounts attributable to non-controlling interests, which are not material for further disclosure. Foreign currency translation (i) Derivative instruments (i) Defined pension and post-retirement benefit costs (ii) Total 2021 2020 2021 2020 2021 2020 2021 2020 Balance at December 31, 2020 and 2019, respectively $ (400 ) $ (538 ) $ 9 $ 13 $ (1,968 ) $ (1,702 ) $ (2,359 ) $ (2,227 ) Other comprehensive income/(loss) before reclassifications (42 ) (208 ) 7 (19 ) 1 (4 ) (34 ) (231 ) Loss/(gain) reclassified from accumulated other comprehensive loss (net of income tax benefit of $6 and $0, respectively) (iii) 44 — (1 ) 1 39 11 82 12 Net current-period other comprehensive income/(loss) 2 (208 ) 6 (18 ) 40 7 48 (219 ) Balance at March 31, 2021 and 2020, respectively $ (398 ) $ (746 ) $ 15 $ (5 ) $ (1,928 ) $ (1,695 ) $ (2,311 ) $ (2,446 ) (i) Reclassification adjustments from accumulated other comprehensive loss related to derivative instruments are included in Revenue and Salaries and benefits in the accompanying condensed consolidated statements of comprehensive income. See Note 8 — Derivative Financial Instruments for additional details regarding the reclassification adjustments for the derivative settlements. (ii) Reclassification adjustments from accumulated other comprehensive loss are included in the computation of net periodic pension cost (see Note 11 — Retirement Benefits). These components are included in Other income, net in the accompanying condensed consolidated statements of comprehensive income. (iii) Includes reclassifications of $44 million and $31 million of foreign currency translation and defined pension and post-retirement benefit costs, respectively, attributable to the gain on disposal of our Miller business (see Note 3 — Divestitures). The net gain on disposal is included in Other income, net in the accompanying condensed consolidated statements of comprehensive income.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	Basic and diluted earnings per share are as follows: Three Months Ended March 31, 2021 2020 Net income attributable to Willis Towers Watson $ 733 $ 305 Basic average number of shares outstanding 130 130 Dilutive effect of potentially issuable shares — — Diluted average number of shares outstanding 130 130 Basic earnings per share $ 5.64 $ 2.36 Dilutive effect of potentially issuable shares (0.01 ) (0.02 ) Diluted earnings per share $ 5.63 $ 2.34

Nature of Operations (Details)

Nature of Operations (Details)	Mar. 31, 2021EmployeeCountry
Minority Interest [Line Items]
Number of employees employed (more than 00,000) | Employee	46,000
Number of countries in which entity operates (more than 140) | Country	140
Proposed Combination with AON Plc [Member]
Minority Interest [Line Items]
Number of shares receivable upon acquisition	1.08
Proposed Combination with AON Plc [Member] | Aon Plc [Member]
Minority Interest [Line Items]
Percentage of ownership by parent	63.00%
Proposed Combination with AON Plc [Member] | Willis Towers Watson Public Limited Company [Member]
Minority Interest [Line Items]
Percentage of ownership by non-controlling owner	37.00%

Divestitures - Miller Divestitu

Divestitures - Miller Divestiture (Details) £ in Millions, $ in Millions	Mar. 01, 2021USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Mar. 01, 2021GBP (£)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Tax exempt gain on sale		$ 359	$ 0
Miller [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Final total consideration received from sale of subsidiary	$ 818			£ 623
Miller [Member] | Other Income, Net [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Tax exempt gain on sale	$ 356

Divestitures - Max Matthiessen

Divestitures - Max Matthiessen Divestiture (Details) kr in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Sep. 30, 2020USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2020SEK (kr)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Tax exempt gain on sale		$ 359	$ 0
Max Matthiessen [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total consideration received from sale of subsidiary	$ 262			kr 2,300
Notes receivable repayable by purchaser	68			kr 600
Max Matthiessen [Member] | Other Income, Net [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Tax exempt gain on sale	$ 86
Max Matthiessen [Member] | Minimum [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Disposal group including discontinued operation notes payable interest rate	5.00%
Max Matthiessen [Member] | Maximum [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Disposal group including discontinued operation notes payable interest rate	10.00%

Revenue - Schedule of Disaggreg

Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 2,562	$ 2,434
Reimbursable expenses and other	[1]	9	27
Interest and other income	[2]	28	32
Total revenue		2,590	2,466
HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		883	855
Reimbursable expenses and other	[1]	11	15
Interest and other income	[2]	3	10
Total revenue		886	865
CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		790	721
Interest and other income	[2]	20	18
Total revenue		810	739
IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		605	615
Reimbursable expenses and other	[1]	1	3
Interest and other income	[2]	1	3
Total revenue		606	618
BDA [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		286	234
Reimbursable expenses and other	[1]	2	3
Interest and other income	[2]	3
Total revenue		289	234
Corporate, Non-Segment
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	(2)	9
Reimbursable expenses and other	[1]	(5)	6
Interest and other income	[1],[2]	1	1
Total revenue	[1]	(1)	10
Broking [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,378	1,262
Broking [Member] | HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		97	83
Broking [Member] | CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		717	648
Broking [Member] | IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		412	433
Broking [Member] | BDA [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		152	98
Consulting [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		763	724
Consulting [Member] | HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		594	582
Consulting [Member] | CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		44	47
Consulting [Member] | IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		123	93
Consulting [Member] | Corporate, Non-Segment
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	2	2
Outsourced administration [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		293	289
Outsourced administration [Member] | HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		132	128
Outsourced administration [Member] | CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		25	25
Outsourced administration [Member] | IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		4	3
Outsourced administration [Member] | BDA [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		132	133
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		119	132
Other [Member] | HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		49	47
Other [Member] | CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		4	1
Other [Member] | IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		65	83
Other [Member] | Corporate, Non-Segment
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	1	1
Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,553	2,407
Service | HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		872	840
Service | CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		790	721
Service | IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		604	612
Service | BDA [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		284	231
Service | Corporate, Non-Segment
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	$ 3	$ 3
[1]	Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the condensed consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations and impacts from hedged revenue transactions.
[2]	Interest and other income is included in segment revenue and total revenue, however it has been presented separately in the above tables because it does not arise directly from contracts with customers.

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 23
December 31 2020 [Member]
Disaggregation Of Revenue [Line Items]
Contract with Customer, Liability, Revenue Recognized	$ 275
Maximum [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue, Percentage of Total Revenue	5.00%	5.00%

Revenue - Schedule of Revenue b

Revenue - Schedule of Revenue by Geography (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 2,562	$ 2,434
Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,553	2,407
Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,553	2,407
Corporate, Non-Segment
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	(2)	9
Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	3	3
HCB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		883	855
HCB [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		872	840
HCB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		872	840
CRB [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		790	721
CRB [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		790	721
CRB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		790	721
IRR [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		605	615
IRR [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		604	612
IRR [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		604	612
BDA [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		286	234
BDA [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		284	231
BDA [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		284	231
North America [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,185	1,110
North America [Member] | Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2	2
North America [Member] | HCB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		468	476
North America [Member] | CRB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		247	233
North America [Member] | IRR [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		186	170
North America [Member] | BDA [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		282	229
Great Britain [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		613	584
Great Britain [Member] | HCB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		147	126
Great Britain [Member] | CRB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		155	137
Great Britain [Member] | IRR [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		311	321
Western Europe [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		492	477
Western Europe [Member] | Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1	1
Western Europe [Member] | HCB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		171	156
Western Europe [Member] | CRB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		261	244
Western Europe [Member] | IRR [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		59	76
International [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		263	236
International [Member] | HCB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		86	82
International [Member] | CRB [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		127	107
International [Member] | IRR [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		48	45
International [Member] | BDA [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 2	$ 2
[1]	Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the condensed consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations and impacts from hedged revenue transactions.

Revenue - Schedule of Contract

Revenue - Schedule of Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Billed Receivable, Current	$ 1,727	$ 1,697
Unbilled Receivable, Current	508	445
Contract asset, Current	334	413
Accounts receivable, net	2,569	2,555
Non-current accounts receivable, net	22	34
Contract asset, Noncurrent	380	329
Deferred revenue	$ 620	$ 549

Revenue - Schedule of Contrac_2

Revenue - Schedule of Contract Balances (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Allowance for doubtful debts	$ 44	$ 41

Revenue - Schedule of Remaining

Revenue - Schedule of Remaining Performance Obligations (Details) $ in Millions	Mar. 31, 2021USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 1,331
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-04-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 429
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 426
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 476
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period

Revenue - Schedule of Remaini_2

Revenue - Schedule of Remaining Performance Obligations (Details1) $ in Millions	Mar. 31, 2021USD ($)
Revenue From Contract With Customer [Abstract]
Revenue, Remaining Performance Obligation	$ 1,331

Segment Information - Narrative

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 31, 2021segment
Segment Reporting [Abstract]
Number of operating segments	4
Number of reportable segments	4

Segment Information - Revenue (

Segment Information - Revenue (Net of Reimbursable Expenses) of the Reported Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 2,590	$ 2,466
Income from operations	452	360
HCB [Member]
Segment Reporting Information [Line Items]
Revenues	886	865
CRB [Member]
Segment Reporting Information [Line Items]
Revenues	810	739
IRR [Member]
Segment Reporting Information [Line Items]
Revenues	606	618
BDA [Member]
Segment Reporting Information [Line Items]
Revenues	289	234
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	2,577	2,435
Income from operations	679	606
Operating Segments [Member] | HCB [Member]
Segment Reporting Information [Line Items]
Revenues	875	850
Income from operations	220	213
Operating Segments [Member] | CRB [Member]
Segment Reporting Information [Line Items]
Revenues	810	739
Income from operations	162	127
Operating Segments [Member] | IRR [Member]
Segment Reporting Information [Line Items]
Revenues	605	615
Income from operations	290	277
Operating Segments [Member] | BDA [Member]
Segment Reporting Information [Line Items]
Revenues	287	231
Income from operations	$ 7	$ (11)

Segment Information - Reconcili

Segment Information - Reconciliation of Information Reported by Segment to Condensed Consolidated Statement of Comprehensive Income Amounts (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Revenue:
Revenue		$ 2,590	$ 2,466
Income/(loss) from operations		452	360
Amortization		(103)	(121)
Interest expense		(59)	(61)
Other income, net		439	92
Income from operations before income taxes		832	391
Operating Segments [Member]
Revenue:
Revenue		2,577	2,435
Income/(loss) from operations		679	606
Segment Reconciling Items [Member]
Revenue:
Revenue		13	31
Amortization		(103)	(121)
Transaction and integration expenses	[1]	(24)	(9)
Unallocated, net	[2]	(100)	(116)
Interest expense		(59)	(61)
Other income, net		$ 439	$ 92
[1]	Includes mainly transaction costs related to the proposed Aon combination.
[2]	Includes certain costs, primarily related to corporate functions which are not directly related to the segments, and certain differences between budgeted expenses determined at the beginning of the year and actual expenses that we report for U.S. GAAP purposes.

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Loss Carryforwards [Line Items]
Provision for income taxes	$ 96	$ 78
Effective tax rate	11.50%	20.00%
Liabilities for uncertain tax positions	$ 49
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Expected decrease in liability for uncertain tax position	4
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Expected decrease in liability for uncertain tax position	$ 8

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Components of Goodwill (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	$ 11,696
Accumulated impairment losses, beginning balance	(492)
Goodwill, net, beginning balance	11,204
Goodwill disposals	(188)
Foreign exchange	(30)
Goodwill, gross, ending balance	11,478
Accumulated impairment losses, ending balance	(492)
Goodwill, net, ending balance	10,986
HCB [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	4,346
Accumulated impairment losses, beginning balance	(130)
Goodwill, net, beginning balance	4,216
Goodwill disposals	0
Foreign exchange	(17)
Goodwill, gross, ending balance	4,329
Accumulated impairment losses, ending balance	(130)
Goodwill, net, ending balance	4,199
CRB [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	2,378
Accumulated impairment losses, beginning balance	(362)
Goodwill, net, beginning balance	2,016
Goodwill disposals	0
Foreign exchange	(16)
Goodwill, gross, ending balance	2,362
Accumulated impairment losses, ending balance	(362)
Goodwill, net, ending balance	2,000
IRR [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	1,694
Accumulated impairment losses, beginning balance	0
Goodwill, net, beginning balance	1,694
Goodwill disposals	(188)
Foreign exchange	3
Goodwill, gross, ending balance	1,509
Accumulated impairment losses, ending balance	0
Goodwill, net, ending balance	1,509
BDA [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	3,278
Accumulated impairment losses, beginning balance	0
Goodwill, net, beginning balance	3,278
Goodwill disposals	0
Foreign exchange	0
Goodwill, gross, ending balance	3,278
Accumulated impairment losses, ending balance	0
Goodwill, net, ending balance	$ 3,278

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Changes in the Net Carrying Amount of the Components of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	$ 5,774		$ 5,988
Finite-lived intangible assets, accumulated amortization	(2,896)		(2,945)
Finite-lived intangible assets, net amount	2,878		3,043
Intangible asset disposals	(54)
Amortization	(103)	$ (121)
Foreign exchange	(8)
Client relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	3,865		4,065
Finite-lived intangible assets, accumulated amortization	(1,956)		(2,031)
Finite-lived intangible assets, net amount	1,909		2,034
Intangible asset disposals	(46)
Amortization	(69)
Foreign exchange	(10)
Software [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	759		761
Finite-lived intangible assets, accumulated amortization	(676)		(659)
Finite-lived intangible assets, net amount	83		102
Intangible asset disposals	0
Amortization	(19)
Foreign exchange	0
Trademark and trade name [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	1,040		1,054
Finite-lived intangible assets, accumulated amortization	(225)		(220)
Finite-lived intangible assets, net amount	815		834
Intangible asset disposals	(8)
Amortization	(11)
Foreign exchange	0
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets, gross carrying amount	110		108
Finite-lived intangible assets, accumulated amortization	(39)		(35)
Finite-lived intangible assets, net amount	71		$ 73
Intangible asset disposals	0
Amortization	(4)
Foreign exchange	$ 2

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Narrative (Details)	3 Months Ended
	Mar. 31, 2021
Finite-lived Intangible Assets [Roll Forward]
Weighted average remaining life of amortizable intangible assets	13 years 4 months 24 days

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Schedule of Future Estimated Amortization Expense for Amortizable Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Remainder of 2021	$ 268
2022	308
2023	257
2024	224
2025	205
Thereafter	1,616
Total	$ 2,878	$ 3,043

Derivative Financial Instrume_3

Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Gains on derivatives to be reclassified within the next twelve months	$ 6
Maximum [Member]
Derivative [Line Items]
Longest outstanding maturity	1 year 8 months 12 days
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Derivative, notional amount	$ 1,500	$ 1,500
Derivative liability, fair value	1
Derivative assets, fair value		15
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Miller [Member]
Derivative [Line Items]
Derivative, notional amount		27
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Derivative, notional amount	249	340
Derivative assets, fair value	$ 8	$ 5

Derivative Financial Instrume_4

Derivative Financial Instruments - Schedule of Derivative Instruments Designated As Hedging Instrument Effect on Condensed Consolidated Statements of Comprehensive Income (Details) - Cash Flow Hedging [Member] - Designated as Hedging Instrument [Member] - Foreign exchange contracts [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Gain/(loss) recognized in OCI (effective element)	$ 4	$ (24)
(Loss)/gain reclassified from Accumulated OCL into income (effective element)	1	(2)
Revenue [Member]
Derivative [Line Items]
(Loss)/gain reclassified from Accumulated OCL into income (effective element)	(2)	0
Salaries and Benefits [Member]
Derivative [Line Items]
(Loss)/gain reclassified from Accumulated OCL into income (effective element)	$ 3	$ (2)

Derivative Financial Instrume_5

Derivative Financial Instruments - Schedule of Derivative Instruments, Effect on Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other income, net [Member] | Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Loss recognized in income	$ (16)	$ (12)

Debt - Schedule of Current and

Debt - Schedule of Current and Long-term Debt (Details) € in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2021USD ($)		Dec. 31, 2020USD ($)		Mar. 31, 2021EUR (€)
Debt Instrument [Line Items]
Current debt		$ 471,000,000		$ 971,000,000
Long-term debt, excluding current maturities		4,632,000,000		4,664,000,000
Revolving 1.25 Billion Dollar Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	[1]	$ 1,250,000,000
Line of credit maturity date		Mar. 7, 2022
5.750% senior notes due 2021 [Member]
Debt Instrument [Line Items]
Current debt				$ 500,000,000
Stated interest rate		5.75%		5.75%		5.75%
Debt instrument maturity year		2021		2021
3.500% senior notes due 2021 [Member]
Debt Instrument [Line Items]
Current debt		$ 450,000,000		$ 449,000,000
Stated interest rate		3.50%		3.50%		3.50%
Debt instrument maturity year		2021		2021
Collateralized Facility [Member]
Debt Instrument [Line Items]
Current portion of long term debt		$ 21,000,000		$ 22,000,000
Long-term debt, excluding current maturities	[2]	27,000,000		33,000,000
Renewal commissions receivables pledged as collateral		$ 92,000,000		$ 98,000,000
2.125% senior notes due 2022 [Member]
Debt Instrument [Line Items]
Stated interest rate		2.125%		2.125%		2.125%
Debt instrument maturity year		2022		2022
Long-term debt, excluding current maturities		$ 633,000,000	[3]	$ 659,000,000	[3]	€ 540
4.625% senior notes due 2023 [Member]
Debt Instrument [Line Items]
Stated interest rate		4.625%		4.625%		4.625%
Debt instrument maturity year		2023		2023
Long-term debt, excluding current maturities		$ 249,000,000		$ 249,000,000
3.600% senior notes due 2024 [Member]
Debt Instrument [Line Items]
Stated interest rate		3.60%		3.60%		3.60%
Debt instrument maturity year		2024		2024
Long-term debt, excluding current maturities		$ 647,000,000		$ 647,000,000
4.400% senior notes due 2026 [Member]
Debt Instrument [Line Items]
Stated interest rate		4.40%		4.40%		4.40%
Debt instrument maturity year		2026		2026
Long-term debt, excluding current maturities		$ 546,000,000		$ 546,000,000
4.500% senior notes due 2028 [Member]
Debt Instrument [Line Items]
Stated interest rate		4.50%		4.50%		4.50%
Debt instrument maturity year		2028		2028
Long-term debt, excluding current maturities		$ 596,000,000		$ 596,000,000
2.950% senior notes due 2029 [Member]
Debt Instrument [Line Items]
Stated interest rate		2.95%		2.95%		2.95%
Debt instrument maturity year		2029		2029
Long-term debt, excluding current maturities		$ 726,000,000		$ 726,000,000
6.125% senior notes due 2043 [Member]
Debt Instrument [Line Items]
Stated interest rate		6.125%		6.125%		6.125%
Debt instrument maturity year		2043		2043
Long-term debt, excluding current maturities		$ 271,000,000		$ 271,000,000
5.050% senior notes due 2048 [Member]
Debt Instrument [Line Items]
Stated interest rate		5.05%		5.05%		5.05%
Debt instrument maturity year		2048		2048
Long-term debt, excluding current maturities		$ 395,000,000		$ 395,000,000
3.875% senior notes due 2049 [Member]
Debt Instrument [Line Items]
Stated interest rate		3.875%		3.875%		3.875%
Debt instrument maturity year		2049		2049
Long-term debt, excluding current maturities		$ 542,000,000		$ 542,000,000
[1]	The $1.25 billion revolving credit facility expires on March 7, 2022.
[2]	At March 31, 2021 and December 31, 2020, the Company had $92 million and $98 million, respectively, of renewal commissions receivables pledged as collateral for this facility
[3]	Notes issued in Euro (€540 million).

Debt - Narrative (Details)

Debt - Narrative (Details) - 5.750% senior notes due 2021 [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Debt instrument principal and interest payment	$ 500
Stated interest rate	5.75%	5.75%

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) $ in Millions		Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Contingent consideration [Member] | Fair Value Inputs, Discount Rate [Member]
Liabilities:
Fair value inputs, weighted-average discount rate		0.1092	0.0946
Contingent consideration [Member] | Fair Value Inputs, Discount Rate [Member] | Minimum [Member]
Liabilities:
Fair value inputs, weighted-average discount rate		0.0353
Contingent consideration [Member] | Fair Value Inputs, Discount Rate [Member] | Maximum [Member]
Liabilities:
Fair value inputs, weighted-average discount rate		0.1300
Recurring [Member]
Assets:
Mutual funds / exchange traded funds		$ 9	$ 8
Derivative financial instruments	[1]	10	27
Liabilities:
Contingent consideration	[2]	28	45
Derivative financial instruments	[1]	3	7
Recurring [Member] | Level 1 [Member]
Assets:
Mutual funds / exchange traded funds		9	8
Derivative financial instruments	[1]	0	0
Liabilities:
Contingent consideration	[2]	0	0
Derivative financial instruments	[1]	0	0
Recurring [Member] | Level 2 [Member]
Assets:
Mutual funds / exchange traded funds		0	0
Derivative financial instruments	[1]	10	27
Liabilities:
Contingent consideration	[2]	0	0
Derivative financial instruments	[1]	3	7
Recurring [Member] | Level 3 [Member]
Assets:
Mutual funds / exchange traded funds		0	0
Derivative financial instruments	[1]	0	0
Liabilities:
Contingent consideration	[2]	28	45
Derivative financial instruments	[1]	$ 0	$ 0
[1]	See Note 8 — Derivative Financial Instruments for further information on our derivative investments.
[2]	Probability weightings are based on our knowledge of the past and planned performance of the acquired entity to which the contingent consideration applies. The fair value weighted-average discount rates used on our material contingent consideration calculations were 10.92% and 9.46% at March 31, 2021 and December 31, 2020, respectively. The range of these discount rates was 3.53% - 13.00% at March 31, 2021. Using different probability weightings and discount rates could result in an increase or decrease of the contingent consideration payable.

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Liabilities Measured Using Significant Unobservable Inputs Level 3 (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of beginning of period	$ 45
Payments	(17)
Balance as of end of period	$ 28

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details)	3 Months Ended
	Mar. 31, 2021USD ($)
Fair Value Disclosures [Abstract]
Fair value significant transfers to or from Level 3	$ 0

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Liabilities Whose Carrying Values Differ From the Fair Value and are Not Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current debt	$ 471	$ 971
Long-term debt	4,632	4,664
Carrying Value [Member] | Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term note receivable	67	71
Current debt	471	971
Long-term debt	4,632	4,664
Fair Value [Member] | Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term note receivable	69	73
Current debt	476	985
Long-term debt	$ 5,141	$ 5,488

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Compensation and Retirement Disclosure [Line Items]
Portion of pension and OPEB obligation attributed to disclosed plans (as a percent)	99.00%
Defined contribution plan, employer contribution	$ 43,000,000	$ 43,000,000
Pension Plan [Member] | United States [Member]
Compensation and Retirement Disclosure [Line Items]
Defined benefit pension plans, employer contributions	60,000,000
Defined benefit plan, estimated future employer additional contributions, remainder of fiscal year	0
Pension Plan [Member] | United Kingdom [Member]
Compensation and Retirement Disclosure [Line Items]
Defined benefit pension plans, employer contributions	10,000,000
Defined benefit plan, estimated future employer additional contributions, remainder of fiscal year	31,000,000
Pension Plan [Member] | Other Foreign Plans [Member]
Compensation and Retirement Disclosure [Line Items]
Defined benefit pension plans, employer contributions	16,000,000
Defined benefit plan, estimated future employer additional contributions, remainder of fiscal year	$ 9,000,000

Retirement Benefits - Net Perio

Retirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plan [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 20	$ 18
Interest cost	23	33
Expected return on plan assets	(77)	(73)
Settlement	1	0
Amortization of net loss	11	9
Amortization of prior service credit	0	0
Net periodic benefit (income)/cost	(22)	(13)
Pension Plan [Member] | United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4
Interest cost	14	18
Expected return on plan assets	(43)	(62)
Settlement	0	0
Amortization of net loss	7	6
Amortization of prior service credit	(4)	(4)
Net periodic benefit (income)/cost	(22)	(38)
Pension Plan [Member] | Other Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5
Interest cost	3	4
Expected return on plan assets	(9)	(8)
Settlement	0	0
Amortization of net loss	1	0
Amortization of prior service credit	0	0
Net periodic benefit (income)/cost	1	1
PRW [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	1
Expected return on plan assets	0	0
Settlement	0	0
Amortization of net loss	0	0
Amortization of prior service credit	(1)	(1)
Net periodic benefit (income)/cost	$ (1)	$ 0

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Costs Recorded in Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Finance lease cost:
Amortization of right-of-use assets		$ 1
Interest on lease liabilities	$ 1	1
Operating lease cost	46	47
Variable lease cost	13	10
Sublease income	(5)	(5)
Total lease cost, net	$ 55	$ 54

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	Nov. 19, 2020	Feb. 28, 2021	Dec. 31, 2020	Mar. 31, 2021
Loss Contingencies [Line Items]
Insurance recovery receivables			$ 25	$ 2
Settled Litigation [Member] | Merger-Related Securities Litigation [Member]
Loss Contingencies [Line Items]
Litigation settlement amount		$ 90
Provision for litigation losses			65
Insurance recovery receivables			$ 25
Settled Litigation [Member] | Merger-Related Securities Litigation [Member] | Federal Action [Member]
Loss Contingencies [Line Items]
Litigation settlement amount	$ 75
Settled Litigation [Member] | Merger-Related Securities Litigation [Member] | Delaware Action [Member]
Loss Contingencies [Line Items]
Litigation settlement amount	$ 15

Supplementary Information for_3

Supplementary Information for Certain Balance Sheet Accounts - Prepaid and Other Current Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Prepayments and accrued income	$ 138	$ 124
Deferred contract costs	74	108
Derivatives and investments	26	42
Deferred compensation plan assets	13	14
Retention incentives	7	3
Corporate income and other taxes	99	83
Insurance and other recovery receivables	2	25
Restricted cash	6	7	$ 8	$ 8
Acquired renewal commissions receivable	14	16
Other current assets	53	75
Total prepaid and other current assets	$ 432	$ 497

Supplementary Information for_4

Supplementary Information for Certain Balance Sheet Accounts - Deferred Revenue and Accrued Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accounts payable, accrued liabilities and deferred income	$ 913	$ 862
Accrued discretionary and incentive compensation	383	851
Litigation settlements		210
Accrued vacation	182	161
Other employee-related liabilities	48	77
Total deferred revenue and accrued expenses	$ 1,526	$ 2,161

Supplementary Information for_5

Supplementary Information for Certain Balance Sheet Accounts - Provision For Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Claims, lawsuits and other proceedings	$ 316	$ 325
Other provisions	74	82
Total provision for liabilities	$ 390	$ 407

Other Income, Net (Details)

Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Income And Expenses [Abstract]
Gain on disposal of operations	$ 359	$ 0
Net periodic pension and postretirement benefit credits	76	76
Interest in earnings of associates and other investments	2	2
Foreign exchange gain	2	12
Other	0	2
Other income, net	$ 439	$ 92

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity attributable to parent, beginning balance	$ 10,820
Stockholders' equity attributable to parent, ending balance	11,526
Foreign currency translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity attributable to parent, beginning balance	(400)	$ (538)
Other comprehensive income/(loss) before reclassifications	(42)	(208)
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	44	0
Net current-period other comprehensive income/(loss)	2	(208)
Stockholders' equity attributable to parent, ending balance	(398)	(746)
Derivative instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity attributable to parent, beginning balance	9	13
Other comprehensive income/(loss) before reclassifications	7	(19)
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	(1)	1
Net current-period other comprehensive income/(loss)	6	(18)
Stockholders' equity attributable to parent, ending balance	15	(5)
Defined pension and post-retirement benefit costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity attributable to parent, beginning balance	(1,968)	(1,702)
Other comprehensive income/(loss) before reclassifications	1	(4)
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	39	11
Net current-period other comprehensive income/(loss)	40	7
Stockholders' equity attributable to parent, ending balance	(1,928)	(1,695)
Total [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity attributable to parent, beginning balance	(2,359)	(2,227)
Other comprehensive income/(loss) before reclassifications	(34)	(231)
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	82	12
Net current-period other comprehensive income/(loss)	48	(219)
Stockholders' equity attributable to parent, ending balance	$ (2,311)	$ (2,446)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, Current Period, Tax	$ 6	$ 0
Miller [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications of foreign currency translation	44
Reclassifications of defined pension and post-retirement benefits costs	$ 31

Earnings Per Share - Narrative

Earnings Per Share - Narrative (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restricted share units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Antidilutive securities excluded from computation of earnings per share	0.2	0
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	0
Time-based award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding	0.1	0.2
Performance-Based Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding	0.3	0.3
Restricted share units outstanding	0.5	0.3

Earnings Per Share - Basic and

Earnings Per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income attributable to Willis Towers Watson	$ 733	$ 305
Basic average number of shares outstanding (shares)	130	130
Dilutive effect of potentially issuable shares (shares)	0	0
Diluted average number of shares outstanding (shares)	130	130
Basic earnings per share	$ 5.64	$ 2.36
Dilutive effect of potentially issuable shares (USD per share)	(0.01)	(0.02)
Diluted earnings per share	$ 5.63	$ 2.34