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, 2016	Dec. 31, 2015	Dec. 31, 2014
Actuarial (loss) gain arising during the period	$ 134	$ 57	$ 240
Prior service credit arising during the period	234	3	0
Amortization of actuarial net loss	46	70	39
Amortization of prior service credit	(7)	1	3
Total recognized in other comprehensive income	139	$ 17	$ (198)
Qualified Plan
Actuarial (loss) gain arising during the period	124
Prior service credit arising during the period	(200)
Amortization of actuarial net loss	38
Amortization of prior service credit	(2)
Total recognized in other comprehensive income	112
Non-Qualified Plan
Actuarial (loss) gain arising during the period	11
Prior service credit arising during the period	(34)
Amortization of actuarial net loss	7
Amortization of prior service credit	(5)
Total recognized in other comprehensive income	25
Postretirement Benefit Plan
Actuarial (loss) gain arising during the period	(1)
Prior service credit arising during the period	0
Amortization of actuarial net loss	1
Amortization of prior service credit	0
Total recognized in other comprehensive income	$ 2