Retirement Plans (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Oct. 15, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jun. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation				$ 227	$ 449
Defined Benefit Plan, Settlements Benefit obligation threshold				216	224
Pension settlement costs		$ 9	$ 15	34	77
Other comprehensive income, Recognition of net actuarial loss for pension settlement costs, before tax			15	34	77
Liability, Retirement and Postemployment Benefits		564	717	564	717	$ 689	$ 711
Capitalization of pension and OPEB expense related to engineering and plant construction				20	20
Contribution of Property				37
Defined benefit plan, cash contributions by employer				135
Plan assets		2,567		2,567		$ 2,674
Decrease in pension assets				$ 107
Percentage of increase in pension plan				4.00%
Negative investment returns				$ (31)
Benefit payments				274
Pension Costs/Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs		9	$ 15	34	$ 77
Contribution of Property				37
Plan contributions required, 2018		$ 150		150
Plan contributions				135
Defined benefit plan, cash contributions by employer				$ 98
Pension Costs/Benefits [Member] | Subsequent Event [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, cash contributions by employer	$ 15