Benefit Plans (Schedule of Components of Net Periodic Pension Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 86	$ 68	$ 86
Interest cost	337	345	314
Expected return on plan assets	(539)	(518)	(493)
Amortization of net loss	234	147	271
Amortization of prior service cost (credit)	7	10	10
Termination and settlement	8	0	7
Net periodic benefit costs	133	52	195
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	18	15	18
Interest cost	100	107	99
Expected return on plan assets	0	0	0
Amortization of net loss	43	22	51
Amortization of prior service cost (credit)	(39)	(43)	(45)
Termination and settlement	0	0	0
Net periodic benefit costs	$ 122	$ 101	$ 123