Benefit Plans (Components of net periodic cost (benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain		$ (86)
Settlement loss		84
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	9	$ 12
Interest cost on projected benefit obligation	112	132	121
Expected return on plan assets	(174)	(191)	(181)
Amortization of net actuarial (gain) loss	34	25	47
Settlement loss	0	84	3
Net periodic (benefit) cost	(24)	59	2
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1
Interest cost on projected benefit obligation	1	1	1
Amortization of prior service credit	(3)	(10)	(18)
Amortization of net actuarial (gain) loss	1	1	2
Curtailment gain	0	(86)	0
Net periodic (benefit) cost	$ (1)	$ (94)	$ (14)