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, 2019	Dec. 31, 2018	Dec. 31, 2017
Actuarial gain (loss) arising during the period	$ 163	$ (191)	$ 72
Amortization of net actuarial loss	42	61	51
Amortization of prior service credit	(27)	(27)	(27)
Total recognized in other comprehensive income (loss)	178	$ (157)	$ 96
Qualified Plan
Actuarial gain (loss) arising during the period	190
Amortization of net actuarial loss	34
Amortization of prior service credit	(19)
Total recognized in other comprehensive income (loss)	205
Non-Qualified Plan
Actuarial gain (loss) arising during the period	(25)
Amortization of net actuarial loss	7
Amortization of prior service credit	(8)
Total recognized in other comprehensive income (loss)	(26)
Postretirement Benefit Plan
Actuarial gain (loss) arising during the period	(2)
Amortization of net actuarial loss	1
Amortization of prior service credit	0
Total recognized in other comprehensive income (loss)	$ (1)