EBP Plan Assets (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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%
Fair value, plan assets, Level 1 to Level 2 transfers, amount	$ 0
Fair value, plan assets, Level 2 to Level 1 transfers, amount	$ 0
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	10 days
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average duration of fixed income security portfolio	13 years	12 years
Pension Benefits [Member]
Fair values of plan assets
Total assets at fair value	$ 1,132	$ 1,227	$ 1,254
Pension Benefits [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan asset target allocation	25.00%
Pension Benefits [Member] | Fixed Income Securities [Member]
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	$ 219	236
Pension Benefits [Member] | Level 1 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	10	17
Pension Benefits [Member] | Level 1 [Member] | Equity securities - U.S. large cap
Fair values of plan assets
Total assets at fair value	30	62
Pension Benefits [Member] | Level 1 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	22	54
Pension Benefits [Member] | Level 1 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	157	103
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] | Insurance company investment contracts and other
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 2 [Member]
Fair values of plan assets
Total assets at fair value	285	225
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 - U.S. large cap
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 2 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	0	0
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	21	15
Pension Benefits [Member] | Level 2 [Member] | Fixed income securities - Mortgage and asset-backed securities
Fair values of plan assets
Total assets at fair value	48	47
Pension Benefits [Member] | Level 2 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	210	158
Pension Benefits [Member] | Level 2 [Member] | Insurance company investment contracts and other
Fair values of plan assets
Total assets at fair value	6	5
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 - U.S. large cap
Fair values of plan assets
Total assets at fair value	0	0
Pension Benefits [Member] | Level 3 [Member] | Equity securities - U.S. small cap
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] | Insurance company investment contracts and 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	504	461
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	10	17
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity securities - U.S. large cap
Fair values of plan assets
Total assets at fair value	30	62
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	22	54
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	157	103
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	21	15
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	48	47
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	210	158
Pension Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Insurance company investment contracts and other
Fair values of plan assets
Total assets at fair value	6	5
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	123	265
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - International small cap
Fair values of plan assets
Total assets at fair value	8	26
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	19	41
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - International developed markets
Fair values of plan assets
Total assets at fair value	51	110
Pension Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - fixed income - U.S. long duration
Fair values of plan assets
Total assets at fair value	335	205
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	$ 92	119
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Proportion of assets subjected to income tax	38.00%
Fair values of plan assets
Total assets at fair value	$ 214	227	$ 208
Other Postretirement Benefits [Member] | Level 1 [Member]
Fair values of plan assets
Total assets at fair value	102	105
Other Postretirement Benefits [Member] | Level 1 [Member] | Cash management fund
Fair values of plan assets
Total assets at fair value	11	11
Other Postretirement Benefits [Member] | Level 1 [Member] | Equity securities - U.S. large cap
Fair values of plan assets
Total assets at fair value	20	25
Other Postretirement Benefits [Member] | Level 1 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	9	14
Other Postretirement Benefits [Member] | Level 1 [Member] | Equity securities - International developed markets large cap growth
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 1 [Member] | Fixed income securities - U.S. Treasury securities
Fair values of plan assets
Total assets at fair value	19	12
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	43	43
Other Postretirement Benefits [Member] | Level 2 [Member]
Fair values of plan assets
Total assets at fair value	38	32
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 - U.S. large cap
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 2 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 2 [Member] | Equity securities - International developed markets large cap growth
Fair values of plan assets
Total assets at fair value	5	6
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	2	2
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	6	5
Other Postretirement Benefits [Member] | Level 2 [Member] | Fixed income securities - Corporate bonds
Fair values of plan assets
Total assets at fair value	25	19
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 - U.S. large cap
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	0	0
Other Postretirement Benefits [Member] | Level 3 [Member] | Equity securities - International developed markets large cap growth
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	140	137
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	11	11
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity securities - U.S. large cap
Fair values of plan assets
Total assets at fair value	20	25
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity securities - U.S. small cap
Fair values of plan assets
Total assets at fair value	9	14
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Equity securities - International developed markets large cap growth
Fair values of plan assets
Total assets at fair value	5	6
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	19	12
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	2	2
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	6	5
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	25	19
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	43	43
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	14	31
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - International small cap
Fair values of plan assets
Total assets at fair value	1	3
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	2	5
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - equities - International developed markets
Fair values of plan assets
Total assets at fair value	6	13
Other Postretirement Benefits [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Commingled investment funds - fixed income - U.S. long duration
Fair values of plan assets
Total assets at fair value	40	24
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	$ 11	$ 14