EBP Plan Assets (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of total stock portfolio invested in the common stock of any one corporation	5.00%
Maximum percentage of portfolio invested in fixed income securities of any one issuer with exception of bond index funds and U. S. government guaranteed and agency securities	5.00%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	30 days
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	1 day
Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Weighted average duration of fixed income security portfolio	16 years	14 years
Pension Benefits [Member]
Fair values of plan assets
Total assets at fair value	$ 1,357	$ 1,299	$ 1,132
Pension Benefits [Member] | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset target allocation	25.00%
Pension Benefits [Member] | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset target allocation	75.00%
Pension Benefits [Member] | Level 1 [Member]
Fair values of plan assets
Total assets at fair value	$ 170	119
Pension Benefits [Member] | Level 1 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	21	11
Pension Benefits [Member] | Level 1 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	39	41
Pension Benefits [Member] | Level 1 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	110	62
Pension Benefits [Member] | Level 1 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 1 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 1 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 1 [Member] | Other
Fair values of plan assets
Total assets at fair value	0	5
Pension Benefits [Member] | Level 2 [Member]
Fair values of plan assets
Total assets at fair value	419	432
Pension Benefits [Member] | Level 2 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 2 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	22	22
Pension Benefits [Member] | Level 2 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 2 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	32	35
Pension Benefits [Member] | Level 2 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	19	11
Pension Benefits [Member] | Level 2 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	342	360
Pension Benefits [Member] | Level 2 [Member] | Other
Fair values of plan assets
Total assets at fair value	4	4
Pension Benefits [Member] | Level 3 [Member]
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Other
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Fair values of plan assets
Total assets at fair value	589	551
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	21	11
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	61	63
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	110	62
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	32	35
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	19	11
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	342	360
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Other
Fair values of plan assets
Total assets at fair value	4	9
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - U.S. large cap
Fair values of plan assets
Total assets at fair value	137	133
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - Global large and mid cap
Fair values of plan assets
Total assets at fair value	121	100
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - International emerging markets
Fair values of plan assets
Total assets at fair value	30	26
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - fixed income - U.S. long and intermediate duration
Fair values of plan assets
Total assets at fair value	346	380
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - fixed income - Corporate bonds
Fair values of plan assets
Total assets at fair value	134	109
Other Postretirement Benefits [Member]
Fair values of plan assets
Total assets at fair value	278	247	$ 214
Other Postretirement Benefits [Member] | Level 1 [Member]
Fair values of plan assets
Total assets at fair value	116	100
Other Postretirement Benefits [Member] | Level 1 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	12	11
Other Postretirement Benefits [Member] | Level 1 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	38	35
Other Postretirement Benefits [Member] | Level 1 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	14	8
Other Postretirement Benefits [Member] | Level 1 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 1 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 1 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 1 [Member] | Mutual fund - Municipal bonds
Fair values of plan assets
Total assets at fair value	52	46
Other Postretirement Benefits [Member] | Level 2 [Member]
Fair values of plan assets
Total assets at fair value	62	57
Other Postretirement Benefits [Member] | Level 2 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 2 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	10	9
Other Postretirement Benefits [Member] | Level 2 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 2 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	4	4
Other Postretirement Benefits [Member] | Level 2 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	3	1
Other Postretirement Benefits [Member] | Level 2 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	45	43
Other Postretirement Benefits [Member] | Level 2 [Member] | Mutual fund - Municipal bonds
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member]
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Mutual fund - Municipal bonds
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Fair values of plan assets
Total assets at fair value	178	157
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	12	11
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity Securities
Fair values of plan assets
Total assets at fair value	48	44
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	14	8
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - Government and municipal bonds
Fair values of plan assets
Total assets at fair value	4	4
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	3	1
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	45	43
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Mutual fund - Municipal bonds
Fair values of plan assets
Total assets at fair value	52	46
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - U.S. large cap
Fair values of plan assets
Total assets at fair value	18	16
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - Global large and mid cap
Fair values of plan assets
Total assets at fair value	16	12
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - International emerging markets
Fair values of plan assets
Total assets at fair value	4	3
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - fixed income - U.S. long and intermediate duration
Fair values of plan assets
Total assets at fair value	45	46
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - fixed income - Corporate bonds
Fair values of plan assets
Total assets at fair value	$ 17	$ 13