Supplemental Equity and Comprehensive Income Information - Reclass AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Sales or impairments of securities	$ 1,571	$ 1,493
Net of tax	(71)	(35)
Gains (losses) associated with defined benefit pension and postretirement plans amortization
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Prior service benefit	22	23
Net actuarial loss	(141)	(126)
Total before tax	(119)	(103)
Tax effect	36	34
Net of tax	(83)	(69)
Cash flow hedging instruments gains (losses)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total before tax	18	52
Tax effect	(6)	(18)
Net of tax	12	34
Cash flow hedging instruments gains (losses) | Foreign currency forward/option contracts
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	$ 18	53
Cash flow hedging instruments gains (losses) | Interest rate swap contracts
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense		$ (1)