Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 61	$ 57	$ 123	$ 115
Interest costs	89	104	178	208
Expected return on plan assets	(132)	(123)	(264)	(245)
Amortization of net actuarial (gains) losses	44	48	89	96
Amortization of prior service costs (credit)	(4)	(4)	(8)	(8)
Net periodic benefit costs (credit)	58	82	118	166
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	1	1	2	2
Interest costs	11	13	21	26
Expected return on plan assets	(16)	(18)	(31)	(34)
Amortization of net actuarial (gains) losses	(18)	(12)	(37)	(24)
Amortization of prior service costs (credit)	0	(2)	(1)	(5)
Net periodic benefit costs (credit)	$ (22)	$ (18)	$ (46)	$ (35)