Pension and Other Postretirement Employee Benefit Plans - Pretax Pension and OPEB in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2014	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	4 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	$ (3,346)	$ (3,096)
Prior service credit/(cost)	102	68
Accumulated other comprehensive income/(loss), pretax, end of year	(3,244)	(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)	(628)	(513)
Prior service credit/(cost)	11	9
Accumulated other comprehensive income/(loss), pretax, end of year	$ (617)	(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	13 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)	$ 130	109
Prior service credit/(cost)	0	0
Accumulated other comprehensive income/(loss), pretax, end of year	$ 130	$ 109