Benefit Plans (Movements in Other Comprehensive Earnings (Losses)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortization:
Net losses	$ 248	$ 257	$ 267
Prior service cost	5	6	4
Other income/expense:
Net losses	6	4	3
Prior service cost	0	0	1
Deferred income taxes	(31)	(43)	(48)
Amortization of net losses, prior service costs and net transition costs	228	224	227
Other movements during the year:
Deferred income taxes	(17)	78	17
Net gains (losses) and prior service costs	523	(460)	(536)
AOCI Attributable to Noncontrolling Interest [Member]
Other movements during the year:
Net losses	525	(517)	(556)
Prior service cost	13	(18)
Deferred income taxes	(17)	78	17
Net gains (losses) and prior service costs	521	(457)	(539)
Total movements in other comprehensive earnings (losses)	749	(233)	(312)
Pension [Member]
Amortization:
Net losses	175	193	194
Prior service cost	5	6	4
Other income/expense:
Net losses	6	4	3
Prior service cost	0	0	1
Deferred income taxes	(10)	(26)	(26)
Amortization of net losses, prior service costs and net transition costs	176	177	176
Pension [Member] | AOCI Attributable to Noncontrolling Interest [Member]
Other movements during the year:
Net losses	509	(437)	(510)
Prior service cost	13	(18)
Deferred income taxes	(13)	55	4
Net gains (losses) and prior service costs	509	(400)	(506)
Total movements in other comprehensive earnings (losses)	685	(223)	(330)
Postretirement [Member]
Amortization:
Net losses	5	2	4
Prior service cost	0	0	0
Other income/expense:
Net losses	0	0	0
Prior service cost	0	0	0
Deferred income taxes	(1)	0	(2)
Amortization of net losses, prior service costs and net transition costs	4	2	2
Other movements during the year:
Net losses	(12)	(15)	12
Prior service cost	0	0
Deferred income taxes	5	4	(4)
Net gains (losses) and prior service costs	(7)	(11)	8
Total movements in other comprehensive earnings (losses)	(3)	(9)	10
Postemployment [Member]
Amortization:
Net losses	68	62	69
Prior service cost	0	0	0
Other income/expense:
Net losses	0	0	0
Prior service cost	0	0	0
Deferred income taxes	(20)	(17)	(20)
Amortization of net losses, prior service costs and net transition costs	48	45	49
Other movements during the year:
Net losses	28	(65)	(58)
Prior service cost	0	0
Deferred income taxes	(9)	19	17
Net gains (losses) and prior service costs	19	(46)	(41)
Total movements in other comprehensive earnings (losses)	$ 67	$ (1)	$ 8