Pension and Other Postretirement Benefits Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	$ 192		$ 260		$ 343	$ 438
Income Tax Expense (Benefit)	(53)		(88)		(91)	(136)
Net income	141	$ 114	174	$ 131	255	305
Reclassification out of Accumulated Other Comprehensive Income | Defined benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Actuarial losses	19		24		43	49
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	19		31		56	31
Prior service credit	(7)		(9)		(13)	(18)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	0		0		0	(14)
Income before income taxes	31		46		86	48
Income Tax Expense (Benefit)	(3)		(7)		(7)	(8)
Net income	$ 28		$ 39		$ 79	$ 40