Benefit Plans (Schedule of Components of Net Periodic Pension Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Termination, settlement and curtailment	$ 27
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	76	$ 86	$ 68
Interest cost	281	337	345
Expected return on plan assets	(553)	(539)	(518)
Amortization of net loss	171	234	147
Amortization of prior service cost (credit)	5	7	10
Termination, settlement and curtailment	34	8	0
Net periodic benefit cost	14	133	52
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	17	18	15
Interest cost	77	100	107
Expected return on plan assets	0	0	0
Amortization of net loss	25	43	22
Amortization of prior service cost (credit)	(39)	(39)	(43)
Termination, settlement and curtailment	(2)	0	0
Net periodic benefit cost	$ 78	$ 122	$ 101