Employee Benefits Schedule of Fair Value, Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Money Market Funds, at Carrying Value	$ 25	$ 21
Investments, Fair Value Disclosure	0	2
Equity securities:
Domestic	83	52
Defined Benefit Plan, Fair Value of Plan Assets		559
Financial Instruments, Owned, at Fair Value	25	23
Other Postretirement Benefit Plans assets: [Abstract]
Money market funds		4
Domestic equity securities - Other postretirement benefit plan assets at fair value		3
International equity securities - other post retirement assets at fair value		8
Private Equity Funds, Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Money Market Funds, at Carrying Value	5	6
Investments, Fair Value Disclosure	13	18
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure	528	483
Fair Value, Inputs, Level 1 [Member]
Equity securities:
Domestic	83	52
Private equity funds	0	0
Defined Benefit Plan, Fair Value of Plan Assets	83	52
Financial Instruments, Owned, at Fair Value	13	8
Other Postretirement Benefit Plans assets: [Abstract]
Money market funds	3	4
Domestic equity securities - Other postretirement benefit plan assets at fair value	0	0
International equity securities - other post retirement assets at fair value	10	8
Other post retirement benefit plan assets total	13	12
Fair Value, Inputs, Level 2 [Member]
Equity securities:
Domestic	0	0
Private equity funds	0	0
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Financial Instruments, Owned, at Fair Value	19	39
Other Postretirement Benefit Plans assets: [Abstract]
Money market funds	0	0
Domestic equity securities - Other postretirement benefit plan assets at fair value	3	3
International equity securities - other post retirement assets at fair value	0	0
Other post retirement benefit plan assets total	8	7
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Money Market Funds, at Carrying Value	0
Equity securities:
Domestic	0	0
Private equity funds	0	0
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Financial Instruments, Owned, at Fair Value	0	2
Other Postretirement Benefit Plans assets: [Abstract]
Money market funds	0	0
Domestic equity securities - Other postretirement benefit plan assets at fair value	0	0
International equity securities - other post retirement assets at fair value	0	0
Other post retirement benefit plan assets total	0	0
Pension Plan [Member]
Equity securities:
Defined Benefit Plan, Fair Value of Plan Assets	629	559	$ 550
Financial Instruments, Owned, at Fair Value	546	507
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Money Market Funds, at Carrying Value	4	4
Investments, Fair Value Disclosure	8	7
Equity securities:
Defined Benefit Plan, Fair Value of Plan Assets	33	30	$ 30
Financial Instruments, Owned, at Fair Value	12	$ 11
Other Postretirement Benefit Plans assets: [Abstract]
Money market funds	3
Domestic equity securities - Other postretirement benefit plan assets at fair value	3
International equity securities - other post retirement assets at fair value	$ 10