Employee Benefits - Fair Values of Pension Plan Assets by Asset Category (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 1,102	$ 1,046	$ 1,163
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Government bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2	2
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | Common - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	8	6
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | Common - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | Preferred - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3	3
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | Corporate bonds - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	155	157
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | Corporate bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	72	65
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | U.S. Treasury, Agencies, and Corporations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	190	180
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | State and municpal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	27	28
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Pension Plan [Member] | Equity - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2	1
Level 1 [Member] | Government bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 1 [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	13	10
Level 1 [Member] | Pension Plan [Member] | Common - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	8	6
Level 1 [Member] | Pension Plan [Member] | Common - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Level 1 [Member] | Pension Plan [Member] | Preferred - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3	3
Level 1 [Member] | Pension Plan [Member] | Corporate bonds - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 1 [Member] | Pension Plan [Member] | Corporate bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 1 [Member] | Pension Plan [Member] | U.S. Treasury, Agencies, and Corporations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 1 [Member] | Pension Plan [Member] | State and municpal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 1 [Member] | Pension Plan [Member] | Equity - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2	1
Level 2 [Member] | Government bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2	2
Level 2 [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	446	432
Level 2 [Member] | Pension Plan [Member] | Common - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 2 [Member] | Pension Plan [Member] | Common - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Level 2 [Member] | Pension Plan [Member] | Preferred - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 2 [Member] | Pension Plan [Member] | Corporate bonds - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	155	157
Level 2 [Member] | Pension Plan [Member] | Corporate bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	72	65
Level 2 [Member] | Pension Plan [Member] | U.S. Treasury, Agencies, and Corporations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	190	180
Level 2 [Member] | Pension Plan [Member] | State and municpal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	27	28
Level 2 [Member] | Pension Plan [Member] | Equity - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Government bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | Common - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | Common - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Level 3 [Member] | Pension Plan [Member] | Preferred - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | Corporate bonds - US [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | Corporate bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | U.S. Treasury, Agencies, and Corporations [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | State and municpal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Level 3 [Member] | Pension Plan [Member] | Equity - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Pension Plan [Member] | Collective Investment Funds (measured at NAV) [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	584	546
Fair Value Measured at Net Asset Value Per Share [Member] | Pension Plan [Member] | Insurance investment contracts and pooled separate accounts (measured at NAV) [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	16	16
Fair Value Measured at Net Asset Value Per Share [Member] | Pension Plan [Member] | Other assets (measured at NAV) [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 43	$ 42