Pension and Other Postretirement Employee Benefit Plans - Pretax Pension and OPEB in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Percent above which amortization of net gains and losses is included in annual net periodic benefit cost	10.00%
Defined benefit pension plans, U.S.
Defined Benefit Plan Disclosure [Line Items]
Average future service period	7 years
Average remaining amortization period	3 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	$ (3,116)	$ (3,096)
Prior service credit/(cost)	34	68
Accumulated other comprehensive income/(loss), pretax, end of year	(3,082)	(3,028)
Non-U.S. defined benefit pension plans
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	(551)	(513)
Prior service credit/(cost)	8	9
Accumulated other comprehensive income/(loss), pretax, end of year	$ (543)	(504)
OPEB plans
Defined Benefit Plan Disclosure [Line Items]
Percent above which amortization of net gains and losses is included in annual net periodic benefit cost	10.00%
Average future service period	12 years
Average remaining amortization period	2 years
Period over which the firm uses a calculated value that recognizes changes in fair value to determine expected return on plan assets	5 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	$ 138	109
Prior service credit/(cost)	0	0
Accumulated other comprehensive income/(loss), pretax, end of year	$ 138	$ 109