Employee Retirement Plans and Incentive Compensation Plans (Benefit Obligations in Excess of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Cash Balance Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 68	$ 58
Accumulated benefit obligation	67	57
Fair value of plan assets	74	57
Non-Qualified Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	20	19
Accumulated benefit obligation	20	19
Fair value of plan assets	0	0
Post-retirement Health Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	2	2
Accumulated benefit obligation	2	2
Fair value of plan assets	$ 0	$ 0