Employee Benefit Plans (Schedule of Changes, Net of Tax, in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Actuarial gain (loss) arising during the period	$ 142	$ 163	$ (191)
Amortization of net actuarial loss	63	42	61
Amortization of prior service credit	(27)	(27)	(27)
Total recognized in other comprehensive income (loss)	178	$ 178	$ (157)
Qualified Plan
Actuarial gain (loss) arising during the period	153
Amortization of net actuarial loss	54
Amortization of prior service credit	(19)
Total recognized in other comprehensive income (loss)	188
Non-Qualified Plan
Actuarial gain (loss) arising during the period	(22)
Amortization of net actuarial loss	9
Amortization of prior service credit	(8)
Total recognized in other comprehensive income (loss)	(21)
Postretirement Benefit Plan
Actuarial gain (loss) arising during the period	11
Amortization of net actuarial loss	0
Amortization of prior service credit	0
Total recognized in other comprehensive income (loss)	$ 11