Accumulated Other Comprehensive Loss (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Insignificant items	$ 12	$ 5	$ 49
Net of tax	138	113
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net actuarial loss and prior service cost	205	175
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net actuarial loss and prior service cost	12	12
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net actuarial loss and prior service cost	217	187
Income tax benefit	(79)	(75)
Insignificant items		1
Net of tax	$ 138	$ 113