Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Estimated net actuarial loss for the defined benefit pension plan	$ 9
Estimated amortization of prior service credit and transition asset to be reclassified from AOCI	1
Actual return	21	$ 20
Estimated future employer contributions in next fiscal year	24
Other | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Actual return	$ 11