Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 58	$ 62	$ 177	$ 185
Interest costs	89	89	250	267
Curtailment (gains) losses			(17)	0
Expected return on plan assets	(124)	(132)	(381)	(396)
Amortization of net actuarial (gains) losses	38	45	115	134
Amortization of prior service costs (credit)	(6)	(4)	(11)	(12)
Net periodic benefit costs (credit)	55	60	133	178
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	2	2	4	4
Interest costs	9	10	27	31
Curtailment (gains) losses			0	0
Expected return on plan assets	(14)	(15)	(42)	(46)
Amortization of net actuarial (gains) losses	(6)	(19)	(33)	(56)
Amortization of prior service costs (credit)	0	(1)	0	(2)
Net periodic benefit costs (credit)	$ (9)	$ (23)	$ (44)	$ (69)