Accumulated Other Comprehensive Income (Details 1) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ 250	$ 245
Income taxes	(252)	(152)
Prior-service costs	(962)	(657)
NET INCOME	1,369	205
Reclassifications from AOCI | Gains & losses on cash flow hedges
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	(1)	(1)
Net of tax	1	2
Reclassifications from AOCI | Gains & losses on cash flow hedges | Long-term debt
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(2)	(3)
Reclassifications from AOCI | Unrealized gains on AFS securities
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	(1)	(10)
Reclassifications from AOCI | Net prior service costs
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	5	6
Prior-service costs	(18)	(18)
NET INCOME	$ (13)	$ (12)