Restructuring and Other Costs (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				$ (186)
Cost of Sales [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(112)
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(76)
Non-service pension cost (benefit) [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(2)
Otis [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(50)
UTC Climate, Controls & Security [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(52)
Pratt & Whitney [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(3)
UTC Aerospace Systems [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(77)
Eliminations and other [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(4)
Current Year Actions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(97)
Restructuring Reserve	$ 51	$ 48		51
Net pre-tax restructuring costs (reversals)	24	61	$ 12	97
Utilization and foreign exchange	21			46
Expected Costs	180			180
Remaining Costs	83			83
Current Year Actions [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	48	48		48
Net pre-tax restructuring costs (reversals)	19			90
Utilization and foreign exchange	19			42
Current Year Actions [Member] | Facility Exit, Lease Termination and Other Costs
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	3	0		3
Net pre-tax restructuring costs (reversals)	5			7
Utilization and foreign exchange	2			4
Current Year Actions [Member] | Cost of Sales [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(47)
Current Year Actions [Member] | Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(52)
Current Year Actions [Member] | Non-service pension cost (benefit) [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				2
Current Year Actions [Member] | Otis [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	2	18	9
Expected Costs	40			40
Remaining Costs	11			11
Current Year Actions [Member] | UTC Climate, Controls & Security [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	14	23	1
Expected Costs	97			97
Remaining Costs	59			59
Current Year Actions [Member] | Pratt & Whitney [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	0	3	0
Expected Costs	3			3
Remaining Costs	0			0
Current Year Actions [Member] | UTC Aerospace Systems [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	8	15	0
Expected Costs	36			36
Remaining Costs	13			13
Current Year Actions [Member] | Eliminations and other [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	0	(2)	(2)
Expected Costs	4			4
Remaining Costs	0			0
Prior Year Actions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(76)
Restructuring Reserve	52	70		52	$ 85
Net pre-tax restructuring costs (reversals)	9	16	51	76	176
Utilization and foreign exchange	27			109
Expected Costs	368			368
Remaining Costs	116			116
Prior Year Actions [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	57	73		57	84
Net pre-tax restructuring costs (reversals)	3			50
Utilization and foreign exchange	19			77
Prior Year Actions [Member] | Facility Exit, Lease Termination and Other Costs
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	(5)	(3)		(5)	1
Net pre-tax restructuring costs (reversals)	6			26
Utilization and foreign exchange	8			32
Prior Year Actions [Member] | Cost of Sales [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(56)
Prior Year Actions [Member] | Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(20)
Prior Year Actions [Member] | Otis [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	1	4	15		43
Expected Costs	69			69
Remaining Costs	6			6
Prior Year Actions [Member] | UTC Climate, Controls & Security [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	(1)	(5)	7		76
Expected Costs	78			78
Remaining Costs	1			1
Prior Year Actions [Member] | Pratt & Whitney [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	0	0	0		7
Expected Costs	7			7
Remaining Costs	0			0
Prior Year Actions [Member] | UTC Aerospace Systems [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	9	17	29		43
Expected Costs	207			207
Remaining Costs	109			109
Prior Year Actions [Member] | Eliminations and other [Member]
Restructuring Cost and Reserve [Line Items]
Net pre-tax restructuring costs (reversals)	0	$ 0	$ 0		$ 7
Expected Costs	7			7
Remaining Costs	0			0
Two Years Prior Actions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				(13)
Restructuring Reserve	$ 83			$ 83