Retirement Benefits (Tables)

12 Months Ended

Dec. 31, 2021

Retirement Benefits [Abstract]

Schedule of weighted average actuarial assumptions utilized defined benefit plans

The weighted average actuarial assumptions utilized for the U.S. and significant non-U.S. defined benefit plans and post-retirement benefit plans are as follows:

	Pension  Benefits				Post-retirement Benefits
	2021		2020		2021		2020
Weighted average assumptions:
Discount rate (for expense)	1.92	%	2.57	%	2.42	%	2.72	%
Expected return on plan assets	4.73	%	5.31	%	—		—
Rate of compensation increase (for expense)*	1.85	%	1.76	%	—		—
Discount rate (for benefit obligation)	2.28	%	1.92	%	2.36	%	2.42	%
Rate of compensation increase (for benefit obligation)*	2.16	%	1.85	%	—		—

The weighted average actuarial assumptions utilized in determining expense during the year and benefit obligation at the end of the year for the U.S. defined benefit and other U.S. post-retirement plans are as follows:

	U.S. Pension Benefits				U.S. Post-retirement Benefits
	2021		2020		2021		2020
Weighted average assumptions:
Discount rate (for expense)	2.73	%	3.44	%	2.18	%	3.10	%
Expected return on plan assets	7.03	%	7.82	%	—		—
Discount rate (for benefit obligation)	3.00	%	2.73	%	2.56	%	2.18	%

	Non-U.S. Pension Benefits				Non-U.S. Post-retirement Benefits
	2021		2020		2021		2020
Weighted average assumptions:
Discount rate (for expense)	1.49	%	2.09	%	1.96	%	2.53	%
Expected return on plan assets	3.89	%	4.35	%	—		—
Rate of compensation increase (for expense)	2.84	%	2.75	%	—		—
Discount rate (for benefit obligation)	1.89	%	1.49	%	2.28	%	1.96	%
Rate of compensation increase (for benefit obligation)	3.34	%	2.84	%	—		—

Schedule of components of net periodic benefit cost for U.S. defined benefit and other postretirement benefit plans

The components of the net periodic benefit cost for defined benefit and other post-retirement plans are as follows:

Combined U.S. and significant non-U.S. Plans	Pension						Post-retirement
For the Years Ended December 31,	Benefits						Benefits
(In millions)	2021		2020		2019		2021		2020		2019
Service cost	$	38	$	36	$	31	$	1	$	—	$	—
Interest cost	341		421		487		2		3		3
Expected return on plan assets	(832)		(844)		(863)		—		—		—
Amortization of prior service	—		—		—		(2)		(2)		(2)
Recognized actuarial loss (gain)	206		161		104		1		—		(1)
Net periodic benefit (credit) cost	$	(247)	$	(226)	$	(241)	$	2	$	1	$	—
Curtailment loss	2		—		—		—		—		—
Plan termination	—		1		—		—		—		—
Settlement loss	5		3		7		—		—		—
Total (credit) cost	$	(240)	$	(222)	$	(234)	$	2	$	1	$	—

The following table provides the amounts reported in the consolidated statements of income:

Combined U.S. and significant non-U.S. Plans	Pension Benefits						Post-retirement Benefits
For the Years Ended December 31,
(In millions)	2021		2020		2019		2021		2020		2019
Compensation and benefits expense	$	38	$	36	$	31	$	1	$	—	$	—
Other net benefit (credit) cost	(278)		(258)		(265)		1		1		—
Total (credit) cost	$	(240)	$	(222)	$	(234)	$	2	$	1	$	—

The components of the net periodic benefit credit (cost) for the U.S. defined benefit and other post-retirement benefit plans are as follows:

U.S. Plans only	Pension Benefits						Post-retirement Benefits
For the Years Ended December 31,
(In millions)	2021		2020		2019		2021		2020		2019
Interest cost	$	184	$	213	$	241	1		1		1
Expected return on plan assets	(327)		(345)		(343)		—		—		—
Recognized actuarial loss (gain)	90		72		44		(1)		—		(1)
Net periodic benefit (credit) cost	$	(53)	$	(60)	$	(58)	$	—	$	1	$	—

The components of the net periodic benefit cost for the non-U.S. defined benefit and other post-retirement benefit plans and the curtailment, settlement and termination expenses are as follows:

For the Years Ended December 31,	Non-U.S. Pension Benefits						Non-U.S. Post-retirement Benefits
(In millions)	2021		2020		2019		2021		2020		2019
Service cost	$	38	$	36	$	31	$	1	$	—	$	—
Interest cost	157		208		246		1		2		2
Expected return on plan assets	(505)		(499)		(520)		—		—		—
Amortization of prior service credit	—		—		—		(2)		(2)		(2)
Recognized actuarial loss	116		89		60		2		—		—
Net periodic benefit credit	(194)		(166)		(183)		2		—		—
Settlement loss	5		3		7		—		—		—
Curtailment loss	2		—		—		—		—		—
Special termination benefits	—		1		—		—		—		—
Total credit	$	(187)	$	(162)	$	(176)	$	2	$	—	$	—

Schedule of MMC's defined benefit plans and postretirement plans

The following tables provide information concerning the Company’s U.S. defined benefit pension and post-retirement benefit plans:

	U.S. Pension Benefits				U.S. Post-retirement Benefits
(In millions)	2021		2020		2021		2020
Change in benefit obligation:
Benefit obligation at beginning of year	$	6,914	$	6,322	$	31	$	31
Interest cost	184		213		1		1
Employee contributions	—		—		4		4
Plan amendments	1		—		—		—
Actuarial (gain) loss	(227)		650		(1)		1
Benefits paid	(278)		(271)		(7)		(6)
Benefit obligation, December 31	$	6,594	$	6,914	$	28	$	31
Change in plan assets:
Fair value of plan assets at beginning of year	$	5,100	$	4,715	$	2	$	2
Actual return on plan assets	680		591		—		—
Employer contributions	35		65		3		3
Employee contributions	—		—		4		4
Benefits paid	(278)		(271)		(7)		(6)
Other	—		—		—		(1)
Fair value of plan assets, December 31	$	5,537	$	5,100	$	2	$	2
Net funded status, December 31	$	(1,057)	$	(1,814)	$	(26)	$	(29)
Amounts recognized in the consolidated balance sheets:
Current liabilities	$	(31)	$	(30)	$	(1)	$	(1)
Non-current liabilities	(1,026)		(1,784)		(25)		(28)
Net liability recognized, December 31	$	(1,057)	$	(1,814)	$	(26)	$	(29)
Amounts recognized in other comprehensive income (loss):
Prior service cost	$	(1)	$	—	$	—	$	—
Net actuarial (loss) gain	(1,777)		(2,446)		3		3
Total recognized accumulated other comprehensive (loss) income, December 31	$	(1,778)	$	(2,446)	$	3	$	3
Cumulative employer contributions in excess of (less than) net periodic cost	721		632		(29)		(32)
Net amount recognized in consolidated balance sheet	$	(1,057)	$	(1,814)	$	(26)	$	(29)
Accumulated benefit obligation at December 31	$	6,594	$	6,914	$	—	$	—

The following tables provide information concerning the Company’s non-U.S.defined benefit pension and post-retirement benefit plans:

	Non-U.S. Pension Benefits				Non-U.S. Post-retirement Benefits
(In millions)	2021		2020		2021		2020
Change in benefit obligation:
Benefit obligation at beginning of year	$	12,998	$	11,321	$	73	$	61
Service cost	38		36		1		—
Interest cost	157		208		1		2
Employee contributions	2		2		—		—
Actuarial (gain) loss	(617)		1,273		(4)		10
Plan amendments	7		11		—		—
Effect of settlement	(16)		(13)		—		—
Effect of curtailment	(2)		—		—		—
Special termination benefits	—		1		—		—
Benefits paid	(395)		(402)		(3)		(2)
Foreign currency changes	(115)		561		—		2
Benefit obligation, December 31	$	12,057	$	12,998	$	68	$	73
Change in plan assets:
Fair value of plan assets at beginning of year	$	14,028	$	12,313	$	—	$	—
Actual return on plan assets	306		1,415		—		—
Effect of settlement	(16)		(13)		—		—
Company contributions	95		78		3		2
Employee contributions	2		2		—		—
Benefits paid	(395)		(402)		(3)		(2)
Foreign currency changes	(165)		635		—		—
Fair value of plan assets, December 31	$	13,855	$	14,028	$	—	$	—
Net funded status, December 31	$	1,798	$	1,030	$	(68)	$	(73)
Amounts recognized in the consolidated balance sheets:
Non-current assets	$	2,269	$	1,764	$	—	$	—
Current liabilities	(6)		(7)		(3)		(3)
Non-current liabilities	(465)		(727)		(65)		(70)
Net asset (liability) recognized, December 31	$	1,798	$	1,030	$	(68)	$	(73)
Amounts recognized in other comprehensive loss:
Prior service (credit) cost	$	(18)	$	(13)	$	7	$	9
Net actuarial loss	(2,904)		(3,467)		(10)		(16)
Total recognized accumulated other comprehensive (loss) income, December 31	$	(2,922)	$	(3,480)	$	(3)	$	(7)
Cumulative employer contributions in excess of (less than) net periodic cost	4,720		4,510		(65)		(66)
Net asset (liability) recognized in consolidated balance sheets, December 31	$	1,798	$	1,030	$	(68)	$	(73)
Accumulated benefit obligation, December 31	$	11,830	$	12,736	$	—	$	—

Schedule of total recognized in net periodic benefit cost and other comprehensive income (loss)

	U.S. Pension Benefits				U.S. Post-retirement Benefits
(In millions)	2021		2020		2021		2020
Reconciliation of net actuarial (loss) gain recognized in accumulated other comprehensive income (loss):
Beginning balance	$	(2,446)	$	(2,114)	$	3	$	4
Recognized as component of net periodic benefit cost (credit)	90		72		(1)		—
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Other	(1)		—		—		—
Liability experience	227		(650)		1		(1)
Asset experience	353		246		—		—
Total gain (loss) recognized as change in plan assets and benefit obligations	579		(404)		1		(1)
Net actuarial (loss) gain, December 31	$	(1,777)	$	(2,446)	$	3	$	3

	Non-U.S. Pension Benefits				Non-U.S. Post-retirement Benefits
(In millions)	2021		2020		2021		2020
Reconciliation of prior service (cost) credit recognized in accumulated other comprehensive income (loss):
Beginning balance	$	(13)	$	(2)	$	9	$	11
Recognized as component of net periodic benefit credit:
Amortization of prior service credit	—		—		(2)		(2)
Effect of curtailment	2		—		—		—
Total recognized as component of net periodic benefit cost (credit)	2		—		(2)		(2)
Changes in plan assets and benefit obligations recognized in other comprehensive income:
Plan amendments	(7)		(11)		—		—
Prior service (cost) credit, December 31	$	(18)	$	(13)	$	7	$	9

	Non-U.S. Pension Benefits				Non-U.S. Post-retirement Benefits
(In millions)	2021		2020		2021		2020
Reconciliation of net actuarial (loss) gain recognized in accumulated other comprehensive (loss) income:
Beginning balance	$	(3,467)	$	(3,055)	$	(16)	$	(5)
Recognized as component of net periodic benefit cost:
Amortization of net loss	116		89		2		—
Effect of settlement	5		3		—		—
Total recognized as component of net periodic benefit credit	121		92		2		—
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	617		(1,273)		4		(10)
Asset experience	(199)		916		—		—
Effect of curtailment	2		—		—		—
Total amount recognized as change in plan assets and benefit obligations	420		(357)		4		(10)
Exchange rate adjustments	22		(147)		—		(1)
Net actuarial loss, December 31	$	(2,904)	$	(3,467)	$	(10)	$	(16)

Schedule of amounts recognized in other comprehensive income (loss)

For the Years Ended December 31,	U.S. Pension Benefits						U.S. Post-retirement Benefits
(In millions)	2021		2020		2019		2021		2020		2019
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$	(722)	$	272	$	160	$	—	$	2	$	2

For the Years Ended December 31,	Non-U.S. Pension Benefits						Non-U.S. Post-retirement Benefits
(In millions)	2021		2020		2019		2021		2020		2019
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$	(745)	$	261	$	311	$	(2)	$	13	$	5

Schedule of estimated future benefit payments for its pension and postretirement benefits

The estimated future benefit payments for the Company's pension and post-retirement benefit plans are as follows:

For the Years Ended December 31,	Pension Benefits				Post-retirement Benefits
(In millions)	U.S.		Non-U.S.		U.S.		Non-U.S.
2022	$	300	$	349	$	4	$	3
2023	$	312	$	376	$	3	$	3
2024	$	323	$	380	$	3	$	3
2025	$	329	$	391	$	3	$	3
2026	$	335	$	403	$	3	$	3
2027-2031	$	1,719	$	2,225	$	9	$	15

Summary of the U.S. and non-U.S. plans investments measured at fair value on a recurring basis

The following table sets forth, by level within the fair value hierarchy, a summary of the U.S. and non-U.S. plans' investments measured at fair value on a recurring basis at December 31, 2021 and 2020:

	Fair Value Measurements at December 31, 2021
Assets (In millions)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		NAV		Total
Common/collective trusts	$	476	$	—	$	—	$	5,221	$	5,697
Corporate obligations	—		4,209		—		—		4,209
Corporate stocks	2,368		44		1		—		2,413
Private equity/partnerships	—		—		—		1,531		1,531
Government securities	15		7,364		—		—		7,379
Real estate	—		—		—		356		356
Short-term investment funds	681		—		—		—		681
Company common stock	348		—		—		—		348
Other investments	11		6		662		—		679
Total investments	$	3,899	$	11,623	$	663	$	7,108	$	23,293
Net derivative liabilities	—		(3,899)		—		—		(3,899)
Net investments	$	3,899	$	7,724	$	663	$	7,108	$	19,394

	Fair Value Measurements at December 31, 2020
Assets (In millions)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		NAV		Total
Common/collective trusts	$	561	$	—	$	—	$	4,298	$	4,859
Corporate obligations	—		4,707		2		—		4,709
Corporate stocks	2,737		39		1		—		2,777
Private equity/partnerships	—		—		—		1,353		1,353
Government securities	15		4,331		—		—		4,346
Real estate	—		—		—		487		487
Short-term investment funds	1,040		—		—		—		1,040
Company common stock	234		—		—		—		234
Other investments	13		7		771		—		791
Total investments	$	4,600	$	9,084	$	774	$	6,138	$	20,596
Net derivative liabilities	—		(1,522)		—		—		(1,522)
Net investments	$	4,600	$	7,562	$	774	$	6,138	$	19,074

Summary of changes in the fair value of the plans' Level 3 assets

The tables below set forth a summary of changes in the fair value of the plans’ Level 3 assets for the years ended December 31, 2021 and December 31, 2020:

Assets (In millions)	Fair Value, January 1, 2021		Purchases		Sales		Unrealized Gain/ (Loss)		Realized Gain/ (Loss)		Exchange Rate Impact		Transfers in/(out) and Other		Fair Value, December 31, 2021
Other investments	$	773	$	19	$	(15)	$	(78)	$	1	$	(36)	$	(2)	$	662
Corporate stocks	1		1		—		(1)		—		—		—		1
Total assets	$	774	$	20	$	(15)	$	(79)	$	1	$	(36)	$	(2)	$	663

Assets (In millions)	Fair Value, January 1, 2020		Purchases		Sales		Unrealized Gain/ (Loss)		Realized Gain/ (Loss)		Exchange Rate Impact		Transfers in/(out) and Other		Fair Value, December 31, 2020
Other investments	$	682	$	20	$	(12)	$	25	$	1	$	55	$	2	$	773
Corporate stocks	1		—		—		—		—		—		—		1
Total assets	$	683	$	20	$	(12)	$	25	$	1	$	55	$	2	$	774