Postretirement benefit plans - Defined benefit plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended						3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Restructuring charges/other	$ (27)	$ (9)	$ (4)	$ (11)	$ 62	$ 16	$ (282)	$ 15	$ (51)		$ (189)		$ 264
U.S. defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost									21		26		24
Interest cost									45		45		44
Expected return on plan assets									(42)		(48)		(50)
Amortization of prior service cost (credit)									0		1		1
Recognized net actuarial loss									26		21		16
Net periodic benefit costs									50		45		35
Settlement losses									5	[1],[2]	41	[1],[2]	0	[1],[2]
Curtailment gain									0		0		0
Special termination benefit gains									0	[1]	0	[1]	(1)	[1]
Total, including other postretirement losses (gains)									55		86		34
Fair value of benefit obligation	1,076				955				1,076		955		1,098
Fair value of plan assets	1,082				941				1,082		941		1,071
U.S. retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost									4		5		5
Interest cost									22		20		25
Expected return on plan assets									(20)		(24)		(23)
Amortization of prior service cost (credit)									4		4		3
Recognized net actuarial loss									7		11		13
Net periodic benefit costs									17		16		23
Settlement losses									0	[1],[2]	0	[1],[2]	0	[1],[2]
Curtailment gain									0		0		(1)
Special termination benefit gains									0	[1]	0	[1]	0	[1]
Total, including other postretirement losses (gains)									17		16		22
Fair value of benefit obligation	513				472				513		472		509
Fair value of plan assets	497				485				497		485		517
Non-U.S. defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost									39		41		45
Interest cost									68		61		75
Expected return on plan assets									(80)		(67)		(78)
Amortization of prior service cost (credit)									(2)		(3)		(4)
Recognized net actuarial loss									24		31		41
Net periodic benefit costs									49		63		79
Settlement losses									1	[1],[2]	4	[1],[2]	193	[1],[2]
Curtailment gain									(2)		(7)		0
Special termination benefit gains									0	[1]	0	[1]	(337)	[1]
Total, including other postretirement losses (gains)									48		60		(65)
Restructuring charges/other															(144)
Fair value of benefit obligation	2,316				2,276				2,316		2,276		2,414
Fair value of plan assets	2,213				2,179				2,213		2,179		2,218
Non-U.S. defined benefit plan | Difference Between Fair Values of the Obligations Settled and Assets Transferred
Defined Benefit Plan Disclosure [Line Items]
Restructuring charges/other															(337)
Non-U.S. defined benefit plan | Obligation and Assets Transferred to Japan Subsitutional Pension
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit obligation															533
Fair value of plan assets															196
Non-U.S. defined benefit plan | Offset By Settlement Loss Related to Recognition of Previously Unrecognized Actuarial Losses Included In Accumulated Other Comprehensive Income
Defined Benefit Plan Disclosure [Line Items]
Restructuring charges/other															$ 193

[1] Transfer of Japan substitutional pension in 2012: In Japan, we maintain employee pension fund plans (EPFs) pursuant to the Japanese Welfare Pension Insurance Law (JWPIL). An EPF consists of two portions: a substitutional portion based on JWPIL-determined minimum old-age pension benefits similar to Social Security benefits in the United States and a corporate portion established at the discretion of each employer. Employers and employees are exempt from contributing to the Japanese Pension Insurance (JPI) if the substitutional portion is funded by an EPF.The JWPIL was amended to permit each EPF to separate the substitutional portion and transfer those obligations and related assets to the government of Japan. After such a transfer, the employer is required to contribute periodically to JPI, and the government of Japan is responsible for future benefit payments relating to the substitutional portion.During the third quarter of 2012, our EPF received final approval for such a separation and transferred the obligations and assets of its substitutional portion to the government of Japan. On a pre-tax basis, this resulted in a net gain of $144 million recorded in Restructuring charges/other on our Consolidated Statements of Income and included in Other, as shown in Note 4. This net gain of $144 million consisted of two parts - a gain of $337 million, representing the difference between the fair values of the obligations settled of $533 million and the assets transferred from the pension trust to the government of Japan of $196 million, offset by a settlement loss of $193 million related to the recognition of previously unrecognized actuarial losses included in AOCI.

[2] Includes non-restructuring and restructuring-related settlement losses.