Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 72	$ 69
Interest costs	111	105
Curtailment costs	0	0
Expected return on plan assets	(127)	(136)
Amortization of net actuarial (gains) losses	49	48
Amortization of prior service costs (credit)	0	0
Net periodic benefit costs	105	86
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	2	4
Interest costs	21	23
Curtailment costs	30	0
Expected return on plan assets	(18)	(20)
Amortization of net actuarial (gains) losses	2	10
Amortization of prior service costs (credit)	(3)	(1)
Net periodic benefit costs	$ 34	$ 16