Employment Benefit Plans Change in Plan Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Combined Pension and Health and Welfare Benefit Asset / (Liability)		$ (61)		$ 70
Pension and Health and Welfare Benefit Plans, Current Liabilities		34		16
Pension and Health and Welfare Benefit Plans, Other Assets		240		396
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Future Employer Contributions, Next Fiscal Year		0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period		29		0
Employer Contributions	[1]	0		48
Plan participants' contributions		4		4
Benefits paid		(19)		(23)
Fair value of plan assets at measurement date		14		29
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Funded status (plan assets less projected benefit obligations)		(199)		(212)
Pension Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Actual return on plan assets		(189)		479
Fair value of plan assets at beginning of period		2,669	[2]	2,333
Employer Contributions	[3]	15		13
Benefits paid		(149)		(144)
Settlements		(10)		(12)
Fair value of plan assets at measurement date		2,336	[4]	2,669	[2]
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Funded status (plan assets less projected benefit obligations)		138		282
Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period		13
Fair value of plan assets at measurement date		21		13
Fair Value, Inputs, Level 1 [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	[2],[5]	2,644
Fair value of plan assets at measurement date		2,302	[4],[6]	2,644	[2],[5]
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member] | Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period		29
Fair value of plan assets at measurement date		14		29
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	[5]	2
Fair value of plan assets at measurement date		$ 1	[6]	$ 2	[5]

[1] Employer contributions were classified as Other, Net under Operating Activities in the Company’s Consolidated Statements of Cash Flows.

[2] Excludes less than $1 million accrued for dividend and interest receivable.

[3] Employer contributions were classified as Other, Net under Operating Activities in the Company’s Consolidated Statements of Cash Flows.

[4] Excludes less than $1 million accrued for dividend and interest receivable.

[5] See Note 2 to the Consolidated Financial Statements under the heading “Fair Value Measurements” for a definition of each of these levels of inputs.

[6] See Note 2 to the Consolidated Financial Statements under the heading “Fair Value Measurements” for a definition of each of these levels of inputs.