Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 56	$ 61	$ 119	$ 123
Interest costs	83	89	161	178
Curtailment (gains) losses	(17)	0	(17)	0
Expected return on plan assets	(125)	(132)	(257)	(264)
Amortization of net actuarial (gains) losses	39	44	77	89
Amortization of prior service costs (credit)	(1)	(4)	(5)	(8)
Net periodic benefit costs (credit)	35	58	78	118
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	1	1	2	2
Interest costs	10	11	18	21
Curtailment (gains) losses	0	0	0	0
Expected return on plan assets	(14)	(16)	(28)	(31)
Amortization of net actuarial (gains) losses	(7)	(18)	(27)	(37)
Amortization of prior service costs (credit)	0	0	0	(1)
Net periodic benefit costs (credit)	$ (10)	$ (22)	$ (35)	$ (46)