Employee Benefit Plans (Net Periodic Benefit Costs and Other Changes Recognized in OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Periodic Benefit Cost Amortized From Accumulated Other Comprehensive Income (Loss) [Abstract]
Total recognized in OCI	$ (131)	$ (354)	$ 970
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	272	276	262
Interest costs	432	423	456
Settlement and curtailment costs	2	(1)	19
Expected return on plan assets	(535)	(542)	(482)
Amortization of net actuarial (gains) losses	190	191	169
Amortization of prior service costs (credit)	0	(1)	1
Total net periodic benefit costs (credit)	361	346	425
Net Periodic Benefit Cost Amortized From Accumulated Other Comprehensive Income (Loss) [Abstract]
Net actuarial (gains) losses	238	43	960
Prior service costs (credit)	(11)	0	(20)
Amortization of net actuarial (gains) losses	(190)	(191)	(169)
Amortization of prior service (costs) credit	0	1	(1)
Total recognized in OCI	37	(147)	770
Total recognized in net periodic benefit costs and OCI	398	199	1,195
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	9	17	16
Interest costs	84	90	94
Settlement and curtailment costs	31	3	4
Expected return on plan assets	(75)	(80)	(76)
Amortization of net actuarial (gains) losses	9	42	11
Amortization of prior service costs (credit)	(6)	(3)	(1)
Total net periodic benefit costs (credit)	52	69	48
Net Periodic Benefit Cost Amortized From Accumulated Other Comprehensive Income (Loss) [Abstract]
Net actuarial (gains) losses	(124)	(161)	223
Prior service costs (credit)	(41)	(7)	(13)
Amortization of net actuarial (gains) losses	(9)	(42)	(11)
Amortization of prior service (costs) credit	6	3	1
Total recognized in OCI	(168)	(207)	200
Total recognized in net periodic benefit costs and OCI	$ (116)	$ (138)	$ 248