Benefit Obligations (Schedule of Fair Values of Pension Plan Assets) (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets, fair value non-financial receivables		$ 36	$ 25
Pension plan assets, fair value non-financial payables		19	18
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[1]	2,220	2,361
Total liabilities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		(3)	(7)
Swaps [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		(3)	(7)
Defined Benefit Plan, Equity Securities, Non-US [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		59	72
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		2	5
Total plan assets [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[2]	2,223	2,368
Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		595	727
Swaps [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		3	8
Corporate Debt [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		691	776
Treasuries, Other Debt [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		1,420	1,459
Mortgage Backed Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		8	7
Registered Investment Companies [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		54	60
Short-term Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		29	96
Insurance Contracts [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		35	36
Other [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		5	5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[1]	192	129
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total liabilities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaps [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Defined Benefit Plan, Equity Securities, Non-US [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		59	72
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		2	5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total plan assets [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[2]	192	129
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaps [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Debt [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Treasuries, Other Debt [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		127	48
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage Backed Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Insurance Contracts [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		4	4
Significant Other Observable Inputs (Level 2) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[1]	2,028	2,232
Significant Other Observable Inputs (Level 2) [Member] | Total liabilities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		(3)	(7)
Significant Other Observable Inputs (Level 2) [Member] | Swaps [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		(3)	(7)
Significant Other Observable Inputs (Level 2) [Member] | Defined Benefit Plan, Equity Securities, Non-US [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | Defined Benefit Plan, Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | Total plan assets [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[2]	2,031	2,239
Significant Other Observable Inputs (Level 2) [Member] | Swaps [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		3	8
Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		691	776
Significant Other Observable Inputs (Level 2) [Member] | Treasuries, Other Debt [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		1,293	1,411
Significant Other Observable Inputs (Level 2) [Member] | Mortgage Backed Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		8	7
Significant Other Observable Inputs (Level 2) [Member] | Insurance Contracts [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		35	36
Significant Other Observable Inputs (Level 2) [Member] | Other [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		$ 1	$ 1

[1] Total net assets excludes non-financial plan receivables and payables of $36 million and $19 million, respectively, as of December 31, 2018 and $25 million and $18 million, respectively, as of December 31, 2017. Non-financial items include due to/from broker, interest receivables and accrued expenses.

[2] In accordance with ASU 2015-07 (Note 2), certain investments that are measured at fair value using the NAV per share practical expedient have not been classified in the fair value hierarchy. Total investments, at fair value, for the year ended December 31, 2018 excludes investments in common/collective trusts, registered investment companies and short-term investment funds with fair values of $595 million, $54 million and $29 million, respectively. Total investments, at fair value, for the year ended December 31, 2017 excludes investments in common/collective trusts, registered investment companies and short-term investment funds with fair values of $727 million, $60 million and $96 million, respectively.