Postretirement benefits Schedule of Allocation of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	$ 3,002	$ 10,446
Available for sale, Fair Value	80,115	43,587
Equity securities	814	497
Other investments	4,519	3,291
Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	25	$ 25
Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	43
Equity securities	728
Derivative Instruments Fair Value	3
Defined benefit plan, fair value of plan assets excluding measured using NAV	1,579
Pension Plan [Member] | UNITED STATES | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	1,200
Pension Plan [Member] | UNITED STATES | Level 1
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0
Equity securities	728
Derivative Instruments Fair Value	3
Defined benefit plan, fair value of plan assets excluding measured using NAV	937
Pension Plan [Member] | UNITED STATES | Level 2
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	43
Equity securities	0
Derivative Instruments Fair Value	0
Defined benefit plan, fair value of plan assets excluding measured using NAV	637
Pension Plan [Member] | UNITED STATES | Level 3
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0
Equity securities	0
Derivative Instruments Fair Value	0
Defined benefit plan, fair value of plan assets excluding measured using NAV	5
Pension Plan [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	2
Equity securities	512
Defined benefit plan, fair value of plan assets excluding measured using NAV	949
Pension Plan [Member] | Non-US [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	13
Pension Plan [Member] | Non-US [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	2
Equity securities	100
Defined benefit plan, fair value of plan assets excluding measured using NAV	102
Pension Plan [Member] | Non-US [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0
Equity securities	412
Defined benefit plan, fair value of plan assets excluding measured using NAV	847
Pension Plan [Member] | Non-US [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Short-term investments	0
Equity securities	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	318
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 1
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	206
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 2
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	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
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	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
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 2
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	482
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 3
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	5
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	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
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Available for sale, Fair Value	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