Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 67	$ 68	$ 212	$ 206
Interest costs	102	106	322	318
Curtailment costs	(1)	0	(1)	0
Expected return on plan assets	(140)	(136)	(394)	(408)
Amortization of net actuarial (gains) losses	44	48	143	143
Amortization of prior service costs (credit)	0	(1)	0	(1)
Net periodic benefit costs	72	85	282	258
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	4	3	8	12
Interest costs	21	22	63	67
Curtailment costs	(1)	0	26	0
Expected return on plan assets	(19)	(19)	(56)	(59)
Amortization of net actuarial (gains) losses	3	10	7	31
Amortization of prior service costs (credit)	(1)	0	(5)	(2)
Net periodic benefit costs	$ 7	$ 16	$ 43	$ 49