Accumulated Other Comprehensive Income (Details 1) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (255)	$ (262)	$ (858)	$ (751)
Income taxes	(133)	(202)	(503)	(483)
Prior-service costs	(739)	(652)	(2,363)	(1,958)
NET INCOME (LOSS)	(458)	396	1,210	775
Reclassifications from AOCI | Gains & losses on cash flow hedges
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	0	(1)	(1)	(3)
Net of tax	2	3	5	5
Reclassifications from AOCI | Gains & losses on cash flow hedges | Long-term debt
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	2	4	6	8
Reclassifications from AOCI | Unrealized gains on AFS securities
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	0	(21)	(1)	(35)
Reclassifications from AOCI | Net prior service costs
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	5	7	14	21
Prior-service costs	(18)	(19)	(55)	(55)
NET INCOME (LOSS)	$ (13)	$ (12)	$ (41)	$ (34)