Pension and Other Postretirement Benefits Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	$ 178	$ 152
Income Tax Expense (Benefit)	(48)	(39)
Net income	131	113
Reclassification out of Accumulated Other Comprehensive Income | Defined benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Actuarial losses	25	24
Prior service credit	(23)	(12)
Income before income taxes	2	12
Income Tax Expense (Benefit)	(1)	(1)
Net income	$ 1	$ 11