Retirement Plans Fair values of pension plan assets - Level 3 rolforward (Details) - Guaranteed Deposit Account [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan investment sales	$ (12)	$ (19)
Defined Benefit Plan, Plan Assets, Amount	12	9
Defined benefit plan investment purchases	15	17
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 12	$ 9	$ 11