Long-Term Employee Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Re-measurement Impact, Benefit Obligation		$ 527
Defined Benefit Plan, Benefits Paid		$ 550
Other Post Employment Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)			$ 274
Discount rate		3.87%	4.13%	4.60%
Expected return on plan assets		0.00%	0.00%	0.00%
Rate of compensation increase		0.00%	0.00%	0.00%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)			$ 7
Accumulated benefit obligation		$ 24,345	$ 24,984
Discount rate		3.77%	3.93%	4.55%
Expected return on plan assets		7.74%	8.10%	8.35%
Rate of compensation increase		3.96%	4.01%	4.22%
United States Pension Plan of US Entity [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate		4.04%	4.29%	4.90%
Expected return on plan assets		8.00%	8.50%	8.75%
Rate of compensation increase		4.15%	4.20%	4.50%
Scenario, Forecast [Member] | Other Post Employment Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax net loss that will be amortized from accumulated other comprehensive income in next fiscal year	$ 91
Pre-tax prior service cost/(credit) that will be amortized from accumulated other comprehensive income in next fiscal year	(69)
Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax net loss that will be amortized from accumulated other comprehensive income in next fiscal year	758
Pre-tax prior service cost/(credit) that will be amortized from accumulated other comprehensive income in next fiscal year	$ (4)
November 2016 Pension and OPEB Changes [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)		$ 25
November 2016 Pension and OPEB Changes [Member] | Other Post Employment Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)		357
Workforce Reductions [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)		(63)
Workforce Reductions [Member] | Other Post Employment Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)		$ 35