Employee Retirement Plans and Incentive Compensation Plans (Fair Value of Cash Balance Plan) (Details) - Cash Balance Plan - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 74	$ 57
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	74	57
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46	33
Equity mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46	33
Equity mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed income mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21	19
Fixed income mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21	19
Fixed income mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed income mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real estate mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	2
Real estate mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	2
Real estate mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real estate mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2
Other mutual funds [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2
Other mutual funds [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other mutual funds [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0