Employee Benefits (Components of Net Periodic Benefit (Credit) Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 2
Interest cost	20	24
Expected return on plan assets	(31)	(32)
Amortization of actuarial loss	4	5
Net periodic benefit (credit) cost	(6)	(1)
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	0	0
Amortization of actuarial loss	0	0
Net periodic benefit (credit) cost	$ 1	$ 1