Fair Value Measurements - Schedule of Pension Plan Assets at Fair Value by Level (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	$ 2,431	$ 2,833
Total investments in the fair value hierarchy	1,461	1,764
Common Stock
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	750	1,022
Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	7	14
Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	3	2
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	537	537
Government Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	149	169
Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	10	9
Derivatives and other
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	5	11
Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	760	1,038
Total investments in the fair value hierarchy	760	1,038
Level 1 | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	750	1,022
Level 1 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	7	14
Level 1 | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	3	2
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 | Government Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 | Derivatives and other
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	701	726
Total investments in the fair value hierarchy	701	726
Level 2 | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	537	537
Level 2 | Government Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	149	169
Level 2 | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	10	9
Level 2 | Derivatives and other
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	5	11
Investments measured at net asset value (a)
Defined Benefit Plan Disclosure [Line Items]
Investments measured at net asset value	$ 970	$ 1,069