Employee Retirement Plans and Incentive Compensation Plans (Fair Value of Plan Assets and Funded Status) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Cash Balance Plan
Defined Benefit Plan, Amounts recognized in Statement of Financial Position
Fair value of plan assets	$ 74	$ 57
Funded status at the end of the year	6	(1)
Non-Qualified Defined Benefit Plans
Defined Benefit Plan, Amounts recognized in Statement of Financial Position
Fair value of plan assets	0	0
Funded status at the end of the year	(20)	(19)
Post-retirement Health Benefit Plan
Defined Benefit Plan, Amounts recognized in Statement of Financial Position
Fair value of plan assets	0	0
Funded status at the end of the year	$ (2)	$ (2)