Employee Benefits (Components of Net Periodic Benefit (Credit) Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1
Interest cost	18	20
Expected return on plan assets	(31)	(31)
Amortization of actuarial loss	4	4
Net periodic benefit (credit) cost	(8)	(6)
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	1
Expected return on plan assets	0	0
Amortization of actuarial loss	0	0
Net periodic benefit (credit) cost	$ 0	$ 1