Employee Benefits (Components of Net Periodic Benefit (Credit) Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 2	$ 2	$ 4
Interest cost	19	24	59	72
Expected return on plan assets	(30)	(32)	(92)	(95)
Amortization of prior service credit / actuarial (gain) loss	4	5	12	15
Net periodic benefit (credit) cost	(6)	(1)	(19)	(4)
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	2	2
Amortization of prior service credit / actuarial (gain) loss	(1)	0	(1)	0
Net periodic benefit (credit) cost	$ 0	$ 1	$ 1	$ 2