Postretirement benefits Schedule of Allocation of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	$ 3,561	$ 3,002
Available for sale, Fair Value	78,939	80,115
Equity securities	937	814
Other investments	4,672	4,519
Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	15	25
Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	61	43
Equity securities	1,154	728
Derivative Instruments Fair Value		3
Defined benefit plan, fair value of plan assets excluding measured using NAV	2,432	1,579
Pension Plan [Member] | UNITED STATES | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	677	1,200
Pension Plan [Member] | UNITED STATES | Level 1
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	9	0
Equity securities	1,154	728
Derivative Instruments Fair Value		3
Defined benefit plan, fair value of plan assets excluding measured using NAV	1,609	937
Pension Plan [Member] | UNITED STATES | Level 2
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	52	43
Equity securities	0	0
Derivative Instruments Fair Value		0
Defined benefit plan, fair value of plan assets excluding measured using NAV	823	637
Pension Plan [Member] | UNITED STATES | Level 3
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0	0
Equity securities	0	0
Derivative Instruments Fair Value		0
Defined benefit plan, fair value of plan assets excluding measured using NAV	0	5
Pension Plan [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	5	2
Equity securities	614	512
Defined benefit plan, fair value of plan assets excluding measured using NAV	1,075	949
Pension Plan [Member] | Non-US [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	95	13
Pension Plan [Member] | Non-US [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	5	2
Equity securities	122	100
Defined benefit plan, fair value of plan assets excluding measured using NAV	127	102
Pension Plan [Member] | Non-US [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0	0
Equity securities	492	412
Defined benefit plan, fair value of plan assets excluding measured using NAV	948	847
Pension Plan [Member] | Non-US [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0	0
Equity securities	0	0
Defined benefit plan, fair value of plan assets excluding measured using NAV		0
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	525	318
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 1
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	446	206
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 2
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	79	112
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 3
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	0	0
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	692	487
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 1
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	0	0
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 2
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	692	482
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 3
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	0	5
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	456	435
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	0	0
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	456	435
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	$ 0	$ 0