Pension and Other Postretirement Employee Benefit Plans - Pretax Pension and OPEB in AOCI (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
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%
U.S. defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Average future service period	7 years
Average remaining amortization period	5 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	$ (3,346)	$ (1,726)
Prior service credit/(cost)	102	196
Accumulated other comprehensive income/(loss), pretax, end of year	(3,244)	(1,530)
Non-U.S. defined benefit pension plans
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	(628)	(658)
Prior service credit/(cost)	11	14
Accumulated other comprehensive income/(loss), pretax, end of year	(617)	(644)
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
Period over which the firm uses a calculated value that recognizes changes in fair value to determine expected return on plan assets	5 years
Average remaining amortization period	2 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax
Net gain/(loss)	130	125
Prior service credit/(cost)	0	1
Accumulated other comprehensive income/(loss), pretax, end of year	$ 130	$ 126