Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Value of trusts established for certain nonqualified plans	$ 16	$ 22
Projected benefit obligation	234	244
Accumulated benefit obligation in excess of plan assets	211	199
Pension benefits to be funded from the trust	13
Postretirement benefits expected to be funded from cash and cash equivalents	3
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,200	1,200
Employer contributions funded from trust	16	$ 11
Net actuarial loss and prior service cost to be amortized from AOCI into net periodic benefit cost the next fiscal year	$ 18
Assumed compensation increase percentage	4.49%	4.49%	4.49%
Pension Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	70.00%
Pension Benefits [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	20.00%
Pension Benefits [Member] | Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	10.00%
Nonqualified Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions funded from trust	$ 13	$ 11
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions funded from trust	2	$ 2
Net actuarial loss and prior service cost to be amortized from AOCI into net periodic benefit cost the next fiscal year	$ 1
Defined benefit plan health care cost trend rate assumed for next fiscal year	7.50%
Defined benefit plan ultimate health care cost trend rate	5.00%