Retirement Benefits (Tables)

12 Months Ended

Dec. 31, 2012

Defined Benefit Plan Disclosure [Line Items]

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

The Plan’s estimated future benefit payments for its pension and postretirement benefits (without reduction for Medicare subsidy receipts) at December 31, 2012 are as follows:

December 31,	Pension Benefits				Postretirement Benefits
(In millions of dollars)	U.S.		Non-U.S.		U.S.		Non-U.S.
2013	$	210	$	275	$	11	$	4
2014	$	221	$	276	$	11	$	4
2015	$	231	$	287	$	11	$	4
2016	$	242	$	310	$	11	$	4
2017	$	251	$	321	$	11	$	5
2018-2022	$	1,394	$	1,910	$	59	$	27

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

	Fair Value Measurements at December 31, 2012
Assets (In millions of dollars)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Common/Collective trusts	$	16	$	5,376	$	—	$	5,392
Corporate obligations	—		2,236		1		2,237
Corporate stocks	2,005		4		9		2,018
Private equity/Partnerships	2		2		824		828
Government securities	9		309		—		318
Real estate	11		8		357		376
Short-term investment funds	410		4		—		414
Company common stock	276		—		—		276
Other investments	11		112		216		339
Insurance group annuity contracts	—		—		23		23
Swaps	—		4		—		4
Total investments	$	2,740	$	8,055	$	1,430	$	12,225

	Fair Value Measurements at December 31, 2011
Assets (In millions of dollars)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Common/Collective trusts	$	10	$	4,837	$	—	$	4,847
Corporate obligations	—		1,792		1		1,793
Corporate stocks	1,716		15		8		1,739
Private equity/Partnerships	—		1		779		780
Government securities	10		368		—		378
Real estate	14		4		319		337
Short-term investment funds	288		42		—		330
Company common stock	253		—		—		253
Other investments	1		34		202		237
Insurance group annuity contracts	—		—		20		20
Swaps	—		5		—		5
Total investments	$	2,292	$	7,098	$	1,329	$	10,719

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, 2012 and December 31, 2011:

Assets (In millions)	Fair Value, January 1, 2012		Purchases		Sales			Unrealized Gain/ (Loss)		Realized Gain/ (Loss)			Exchange Rate Impact		Transfers in/(out) and Other		Fair Value, December 31, 2012
Private equity/Partnerships	$	779	$	86	$	(79	)	$	138	$	(113	)	$	13	$	—	$	824
Real estate	319		11		(3		)	104		(86		)	12		—		357
Other investments	202		17		(24		)	11		6			4		—		216
Insurance group annuity contracts	20		160		(157		)	1		(1		)	—		—		23
Corporate stocks	8		1		—			—		—			—		—		9
Corporate obligations	1		—		—			—		—			—		—		1
Total assets	$	1,329	$	275	$	(263	)	$	254	$	(194	)	$	29	$	—	$	1,430

Assets (In millions)	Fair Value, January 1, 2011		Purchases		Sales			Unrealized Gain/ (Loss)			Realized Gain/ (Loss)			Exchange Rate Impact			Transfers in/(out) and Other			Fair Value, December 31, 2011
Private equity/Partnerships	$	746	$	119	$	(80	)	$	(83	)	$	70		$	7		$	—		$	779
Real estate	293		—		—			22			(1		)	5			—			319
Other investments	177		32		(13		)	6			2			(2		)	—			202
Insurance group annuity contracts	20		151		(150		)	8			(9		)	—			—			20
Corporate stocks	1		8		—			(1		)	—			—			—			8
Corporate obligations	8		1		(8		)	2			(1		)	—			(1		)	1
Total assets	$	1,245	$	311	$	(251	)	$	(46	)	$	61		$	10		$	(1	)	$	1,329

Combined US & Significant Non-US Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

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 postretirement benefit plans are as follows:

	Pension  Benefits				Postretirement Benefits
	2012		2011		2012		2011
Weighted average assumptions:
Discount rate (for expense)	4.91	%	5.59	%	5.05	%	5.81	%
Expected return on plan assets	8.03	%	8.19	%	—		—
Rate of compensation increase (for expense)	3.09	%	4.08	%	—		—
Discount rate (for benefit obligation)	4.38	%	4.91	%	4.32	%	5.05	%
Rate of compensation increase (for benefit obligation)	2.43	%	3.09	%	—		—

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 postretirement plans are as follows:

Combined U.S. and significant non-U.S. Plans	Pension									Postretirement
For the Years Ended December 31,	Benefits									Benefits
(In millions of dollars)	2012			2011			2010			2012			2011			2010
Service cost	$	240		$	226		$	197		$	5		$	5		$	4
Interest cost	596			609			578			13			13			14
Expected return on plan assets	(905		)	(887		)	(815		)	—			—			—
Amortization of prior service credit	(19		)	(19		)	(21		)	(14		)	(13		)	(13		)
Recognized actuarial loss (credit)	270			215			144			—			(4		)	—
Net periodic benefit cost	$	182		$	144		$	83		$	4		$	1		$	5

U.S. Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule of weighted average actuarial assumptions utilized defined benefit plans

The weighted average actuarial assumptions utilized in determining the above amounts for the U.S. defined benefit and other U.S. postretirement plans as of the end of the year are as follows:

	U.S. Pension Benefits				U.S. Postretirement Benefits
	2012		2011		2012		2011
Weighted average assumptions:
Discount rate (for expense)	5.15	%	5.90	%	5.10	%	5.95	%
Expected return on plan assets	8.75	%	8.75	%	—		—
Rate of compensation increase (for expense)	2.00	%	3.90	%	—		—
Discount rate (for benefit obligation)	4.45	%	5.15	%	4.25	%	5.10	%
Rate of compensation increase (for benefit obligation)	2.00	%	2.00	%	—		—

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 the U.S. defined benefit and other postretirement benefit plans are as follows:

U.S. Plans only	Pension Benefits									Postretirement Benefits
For the Years Ended December 31,
(In millions of dollars)	2012			2011			2010			2012			2011			2010
Service cost	$	93		$	83		$	76		$	3		$	3		$	3
Interest cost	230			231			227			8			8			10
Expected return on plan assets	(322		)	(315		)	(295		)	—			—			—
Amortization of prior service credit	(16		)	(16		)	(18		)	(13		)	(13		)	(13		)
Recognized actuarial loss (credit)	152			100			71			(1		)	(4		)	—
Net periodic benefit cost (credit)	$	137		$	83		$	61		$	(3	)	$	(6	)	$	—

Schedule of MMC's defined benefit plans and postretirement plans

The following schedules provide information concerning the Company’s U.S. defined benefit pension plans and postretirement benefit plans:

	U.S. Pension Benefits						U.S.  Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Change in benefit obligation:
Benefit obligation at beginning of year	$	4,533		$	4,041		$	162		$	180
Service cost	93			83			3			3
Interest cost	230			231			8			8
Actuarial (gain) loss	522			352			13			(20		)
Medicare Part D subsidy	—			—			3			4
Benefits paid	(181		)	(174		)	(13		)	(13		)
Benefit obligation, December 31	$	5,197		$	4,533		$	176		$	162
Change in plan assets:
Fair value of plan assets at beginning of year	$	3,493		$	3,444		$	—		$	—
Actual return on plan assets	500			199			—			—
Employer contributions	124			24			10			9
Medicare Part D subsidy	—			—			3			4
Benefits paid	(181		)	(174		)	(13		)	(13		)
Fair value of plan assets, December 31	$	3,936		$	3,493		$	—		$	—
Net funded status, December 31	$	(1,261	)	$	(1,040	)	$	(176	)	$	(162	)
Amounts recognized in the consolidated balance sheets:
Current liabilities	$	(25	)	$	(124	)	$	(9	)	$	(9	)
Noncurrent liabilities	(1,236		)	(916		)	(167		)	(153		)
Net liability recognized, December 31	$	(1,261	)	$	(1,040	)	$	(176	)	$	(162	)
Amounts recognized in other comprehensive income (loss):
Prior service credit	$	23		$	39		$	—		$	13
Net actuarial (loss) gain	(1,887		)	(1,695		)	(2		)	12
Total recognized accumulated other comprehensive (loss) income, December 31	$	(1,864	)	$	(1,656	)	$	(2	)	$	25
Cumulative employer contributions in excess (deficient) of net periodic cost	603			616			(174		)	(187		)
Net amount recognized in consolidated balance sheet	$	(1,261	)	$	(1,040	)	$	(176	)	$	(162	)
Accumulated benefit obligation at December 31	$	5,114		$	4,467		$	—		$	—

	U.S. Pension Benefits						U.S.  Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of prior service credit (charge) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	39		$	55		$	13		$	26
Recognized as component of net periodic benefit credit	(16		)	(16		)	(13		)	(13		)
Prior service credit, December 31	$	23		$	39		$	—		$	13

Schedule of unrecognized net actuarial gain (loss)

	U.S. Pension Benefits						U.S.  Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of prior service credit (charge) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	39		$	55		$	13		$	26
Recognized as component of net periodic benefit credit	(16		)	(16		)	(13		)	(13		)
Prior service credit, December 31	$	23		$	39		$	—		$	13

	U.S. Pension Benefits						U.S.  Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of net actuarial gain (loss) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	(1,695	)	$	(1,327	)	$	12		$	(4	)
Recognized as component of net periodic benefit cost	152			100			(1		)	(4		)
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	(522		)	(352		)	(13		)	20
Asset experience	178			(116		)	—			—
Total gain (loss) recognized as change in plan assets and benefit obligations	(344		)	(468		)	(13		)	20
Net actuarial gain (loss), December 31	$	(1,887	)	$	(1,695	)	$	(2	)	$	12

For the Years Ended December 31,	U.S. Pension Benefits						U.S. Postretirement Benefits
(In millions of dollars)	2012		2011		2010		2012		2011			2010
Total recognized in net periodic benefit cost and other comprehensive loss (income)	$	346	$	467	$	148	$	24	$	(9	)	$	26

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

	U.S. Pension Benefits						U.S.  Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of net actuarial gain (loss) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	(1,695	)	$	(1,327	)	$	12		$	(4	)
Recognized as component of net periodic benefit cost	152			100			(1		)	(4		)
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	(522		)	(352		)	(13		)	20
Asset experience	178			(116		)	—			—
Total gain (loss) recognized as change in plan assets and benefit obligations	(344		)	(468		)	(13		)	20
Net actuarial gain (loss), December 31	$	(1,887	)	$	(1,695	)	$	(2	)	$	12

For the Years Ended December 31,	U.S. Pension Benefits						U.S. Postretirement Benefits
(In millions of dollars)	2012		2011		2010		2012		2011			2010
Total recognized in net periodic benefit cost and other comprehensive loss (income)	$	346	$	467	$	148	$	24	$	(9	)	$	26

Schedule of change in assumed health care cost trend rates

A one percentage point change in assumed health care cost trend rates would have the following effects:

(In millions of dollars)	1 Percentage Point Increase		1 Percentage Point Decrease
Effect on total of service and interest cost components	$	—	$	—
Effect on postretirement benefit obligation	$	1	$	(5	)

Schedule of estimated amounts that will be amortized from accumulated other comprehensive in the next fiscal year

Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:

	U.S. Pension Benefits			U.S. Postretirement Benefits
(In millions of dollars)	2013			2013
Prior service cost	$	(16	)	$	—
Net actuarial loss	202			—
Projected cost	$	186		$	—

Non-U.S. Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule of weighted average actuarial assumptions utilized defined benefit plans

	Non-U.S. Pension Benefits				Non-U.S. Postretirement Benefits
	2012		2011		2012		2011
Weighted average assumptions:
Discount rate (for expense)	4.77	%	5.41	%	4.95	%	5.51	%
Expected return on plan assets	7.68	%	7.91	%	—		—
Rate of compensation increase (for expense)	3.73	%	4.19	%	—		—
Discount rate (for benefit obligation)	4.33	%	4.77	%	4.45	%	4.95	%
Rate of compensation increase (for benefit obligation)	2.69	%	3.73	%	—		—

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 the non-U.S. defined benefit and other postretirement 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. Postretirement Benefits
(In millions of dollars)	2012			2011			2010			2012			2011		2010
Service cost	$	147		$	143		$	121		$	2		$	2	$	1
Interest cost	366			378			351			5			5		4
Expected return on plan assets	(583		)	(572		)	(520		)	—			—		—
Amortization of prior service cost	(3		)	(3		)	(3		)	(1		)	—		—
Recognized actuarial loss	118			115			73			1			—		—
Net periodic benefit cost	45			61			22			7			7		5
Settlement loss	1			—			5			—			—		—
Curtailment credit	(1		)	—			—			—			—		—
Special termination benefits	—			—			1			—			—		—
Total cost	$	45		$	61		$	28		$	7		$	7	$	5

Schedule of unrecognized net actuarial gain (loss)

	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of prior service credit (cost):
Beginning balance	$	23		$	23		$	1		$	1
Recognized as component of net periodic benefit credit	(3		)	3			(1		)	—
Effect of curtailment	(1		)	—			—			—
Changes in plan assets and benefit obligations recognized in other comprehensive income:
Plan amendments	71			(3		)	—			—
Exchange rate adjustments	3			—			—			—
Prior service credit, December 31	$	93		$	23		$	—		$	1

Schedule of defined benefit plans disclosures and unrecognized net actuarial gain (loss) [Table Text Block]

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

	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Change in benefit obligation:
Benefit obligation at beginning of year	$	7,717		$	6,802		$	91		$	83
Service cost	147			143			2			2
Interest cost	366			378			5			5
Employee contributions	11			14			—			—
Actuarial loss	419			575			10			5
Plan amendments	(71		)	(3		)	—			—
Effect of settlement	(11		)	(7		)	—			—
Effect of curtailment	(3		)	(1		)	(1		)	—
Benefits paid	(278		)	(266		)	(4		)	(4		)
Foreign currency changes	280			66			4			—
Other	2			16			—			—
Benefit obligation at, December 31	$	8,579		$	7,717		$	107		$	91
Change in plan assets:
Fair value of plan assets at beginning of year	$	7,206		$	6,741		$	—		$	—
Actual return on plan assets	721			311			—			—
Effect of settlement	(11		)	(6		)	—			—
Company contributions	389			320			4			4
Employee contributions	11			14			—			—
Benefits paid	(278		)	(266		)	(4		)	(4		)
Foreign currency changes	273			82			—			—
Other	1			10			—			—
Fair value of plan assets, December 31	$	8,312		$	7,206		$	—		$	—
Net funded status, December 31	$	(267	)	$	(511	)	$	(107	)	$	(91	)
Amounts recognized in the consolidated balance sheets:
Non-current assets	$	258		$	39		$	—		$	—
Current liabilities	(6		)	(106		)	(4		)	(4		)
Non-current liabilities	(519		)	(444		)	(103		)	(87		)
Net liability recognized, December 31	$	(267	)	$	(511	)	$	(107	)	$	(91	)
Amounts recognized in other comprehensive income (loss):
Prior service credit	$	93		$	23		$	—		$	1
Net actuarial (loss) gain	(3,309		)	(3,038		)	(27		)	(19		)
Total recognized accumulated other comprehensive (loss) income, December 31	$	(3,216	)	$	(3,015	)	$	(27	)	$	(18	)
Cumulative employer contributions in excess (deficient) of net periodic cost	2,949			2,504			(80		)	(73		)
Net amount recognized in consolidated balance sheet, December 31	$	(267	)	$	(511	)	$	(107	)	$	(91	)
Accumulated benefit obligation, December 31	$	8,229		$	7,246		$	—		$	—

	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of prior service credit (cost):
Beginning balance	$	23		$	23		$	1		$	1
Recognized as component of net periodic benefit credit	(3		)	3			(1		)	—
Effect of curtailment	(1		)	—			—			—
Changes in plan assets and benefit obligations recognized in other comprehensive income:
Plan amendments	71			(3		)	—			—
Exchange rate adjustments	3			—			—			—
Prior service credit, December 31	$	93		$	23		$	—		$	1

	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of net actuarial gain (loss):
Beginning balance	$	(3,038	)	$	(2,305	)	$	(19	)	$	(14	)
Recognized as component of net periodic benefit cost	118			115			1			—
Effect of settlement	1			—			—			—
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	(419		)	(575		)	(10		)	(5		)
Asset experience	138			(261		)	—			—
Effect of curtailment	3			(1		)	1			—
Total amount recognized as change in plan assets and benefit obligations	(278		)	(837		)	(9		)	(5		)
Exchange rate adjustments	(112		)	(11		)	—			—
Net actuarial gain (loss), December 31	$	(3,309	)	$	(3,038	)	$	(27	)	$	(19	)

For the Years Ended December 31,	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012		2011		2010		2012		2011		2010
Total recognized in net periodic benefit cost and other comprehensive loss	$	246	$	792	$	66	$	16	$	12	$	15

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

	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012			2011			2012			2011
Reconciliation of net actuarial gain (loss):
Beginning balance	$	(3,038	)	$	(2,305	)	$	(19	)	$	(14	)
Recognized as component of net periodic benefit cost	118			115			1			—
Effect of settlement	1			—			—			—
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	(419		)	(575		)	(10		)	(5		)
Asset experience	138			(261		)	—			—
Effect of curtailment	3			(1		)	1			—
Total amount recognized as change in plan assets and benefit obligations	(278		)	(837		)	(9		)	(5		)
Exchange rate adjustments	(112		)	(11		)	—			—
Net actuarial gain (loss), December 31	$	(3,309	)	$	(3,038	)	$	(27	)	$	(19	)

For the Years Ended December 31,	Non-U.S. Pension Benefits						Non-U.S. Postretirement Benefits
(In millions of dollars)	2012		2011		2010		2012		2011		2010
Total recognized in net periodic benefit cost and other comprehensive loss	$	246	$	792	$	66	$	16	$	12	$	15

Schedule of change in assumed health care cost trend rates

A one percentage point change in assumed health care cost trend rates would have the following effects:

(In millions of dollars)	1 Percentage Point Increase		1 Percentage Point Decrease
Effect on total of service and interest cost components	$	1	$	(1	)
Effect on postretirement benefit obligation	$	12	$	(10	)

Schedule of estimated amounts that will be amortized from accumulated other comprehensive in the next fiscal year

Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:

	Non-U.S. Pension Benefits			Non-U.S. Postretirement Benefits
(In millions of dollars)	2013			2013
Prior service cost	$	(6	)	$	—
Net actuarial loss	112			2
Projected cost	$	106		$	2