Other Comprehensive Earnings/Losses (Changes in Each Component of Accumulated Other Comprehensive Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			$ 12,770
Other comprehensive losses before reclassifications	$ (216)	$ 48	10	$ (159)
Other comprehensive deferred income taxes	75	(17)	(3)	66
Other comprehensive losses before reclassifications, net of deferred income taxes	(141)	31	7	(93)
Amounts reclassified to net earnings	51	47	159	151
Deferred income taxes	(18)	(16)	(60)	(56)
Amounts reclassified to net earnings, net of deferred income taxes	33	31	99	95
Other comprehensive earnings (losses), net of deferred income taxes	(108)	62	106	2	$ 1,228
Ending balance	12,166		12,166		12,770
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3)	(4)	(4)	(5)	(5)
Other comprehensive losses before reclassifications	0	0	1	1
Other comprehensive deferred income taxes	0	0	0	0
Other comprehensive losses before reclassifications, net of deferred income taxes	0	0	1	1
Amounts reclassified to net earnings	0	0	0	0
Deferred income taxes	0	0	0	0
Amounts reclassified to net earnings, net of deferred income taxes	0	0	0	0
Other comprehensive earnings (losses), net of deferred income taxes	0	0	1	1
Ending balance	(3)	(4)	(3)	(4)	(4)
Benefit Plans [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(1,983)	(2,154)	(2,048)	(2,010)	(2,010)
Other comprehensive losses before reclassifications	0	0	0	(318)
Other comprehensive deferred income taxes	0	0	0	122
Other comprehensive losses before reclassifications, net of deferred income taxes	0	0	0	(196)
Amounts reclassified to net earnings	48	42	154	127
Deferred income taxes	(17)	(14)	(58)	(47)
Amounts reclassified to net earnings, net of deferred income taxes	31	28	96	80
Other comprehensive earnings (losses), net of deferred income taxes	31	28	96	(116)
Ending balance	(1,952)	(2,126)	(1,952)	(2,126)	(2,048)
Accumulated Equity Method Investments Attributable to Parent [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	148	(1,182)	0	(1,265)	(1,265)
Other comprehensive losses before reclassifications	(216)	48	9	158
Other comprehensive deferred income taxes	75	(17)	(3)	(56)
Other comprehensive losses before reclassifications, net of deferred income taxes	(141)	31	6	102
Amounts reclassified to net earnings	3	5	5	24
Deferred income taxes	(1)	(2)	(2)	(9)
Amounts reclassified to net earnings, net of deferred income taxes	2	3	3	15
Other comprehensive earnings (losses), net of deferred income taxes	(139)	34	9	117
Ending balance	9	(1,148)	9	(1,148)	0
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(1,838)	(3,340)	(2,052)	(3,280)	(3,280)
Other comprehensive earnings (losses), net of deferred income taxes			106		1,228
Ending balance	$ (1,946)	$ (3,278)	$ (1,946)	$ (3,278)	$ (2,052)