Pension and Other Employee Benefits (Source of Change in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and PRB Plans [Line Items]
Prior service (cost) credit arising during period	$ (1)	$ (10)	$ (15)
Amortization of prior service cost (credit) included in net income	5	6	4
Actuarial gain (loss) arising during period	(1,886)	(626)	(1,816)
Amortization of net actuarial (gain) loss	1,060	1,362	1,187
Pension and other postretirement benefit plans, net	(822)	1,028	(651)
Pension Plan [Member]
Defined Benefit Plans and PRB Plans [Line Items]
Prior service (cost) credit arising during period	(1)	(10)
Amortization of prior service cost (credit) included in net income	5	6
Net change in prior service (cost) credit not recognized in net income during the period	4	(4)
Actuarial gain (loss) arising during period	(1,847)	(630)
Amortization of net actuarial (gain) loss	1,050	1,351	$ 1,177
Loss recognized due to settlements	1	286
Net change in actuarial gain (loss) not included in net income during the period	(796)	1,007
Effect of exchange rates	(3)	9
Pension and other postretirement benefit plans, net	(795)	1,012
PRB [Member]
Defined Benefit Plans and PRB Plans [Line Items]
Prior service (cost) credit arising during period	0	0
Amortization of prior service cost (credit) included in net income	0	0
Net change in prior service (cost) credit not recognized in net income during the period	0	0
Actuarial gain (loss) arising during period	(39)	4
Amortization of net actuarial (gain) loss	10	11
Loss recognized due to settlements	2	1
Net change in actuarial gain (loss) not included in net income during the period	(27)	16
Effect of exchange rates	0	0
Pension and other postretirement benefit plans, net	$ (27)	$ 16