Benefit Obligations (Schedule of Fair Values of Pension Plan Assets) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets, fair value non-financial receivables		$ 25	$ 19
Pension plan assets, fair value non-financial payables		14	26
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[1]	2,086	2,122
Total liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	278
Swaps [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	270
Other [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	2
Obligations Under Securities Lending [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	6
Total plan assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[2]	2,111	2,400
Cash and Cash quivalents [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		4	6
Equities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		251	278
Swaps [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	275
Other [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	2
US Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		241	249
International Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		327	383
Corporate Debt [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		692	639
Treasuries, Other Debt [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		767	757
Mortgage Backed Securities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		5	31
Registered Investment Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		117	133
Obligations Under Securities Lending [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	6
Short-term Investments [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		43	263
Insurance Contracts [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		32	34
Other [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		18	18
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[1]	615	703
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaps [Member] | Pension Benefits [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 Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Obligations Under Securities Lending [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total plan assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[2]	615	709
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash quivalents [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		4	6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaps [Member] | Pension Benefits [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 Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | US Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		241	249
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | International Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		327	383
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Debt [Member] | Pension Benefits [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 Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	49
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage Backed Securities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Obligations Under Securities Lending [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Insurance Contracts [Member] | Pension Benefits [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 Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		18	16
Significant Other Observable Inputs (Level 2) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[1]	1,471	1,419
Significant Other Observable Inputs (Level 2) [Member] | Total liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	272
Significant Other Observable Inputs (Level 2) [Member] | Swaps [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	270
Significant Other Observable Inputs (Level 2) [Member] | Other [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	2
Significant Other Observable Inputs (Level 2) [Member] | Obligations Under Securities Lending [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | Total plan assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets	[2]	1,496	1,691
Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash quivalents [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | Swaps [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		25	275
Significant Other Observable Inputs (Level 2) [Member] | Other [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	2
Significant Other Observable Inputs (Level 2) [Member] | US Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | International Companies [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		692	639
Significant Other Observable Inputs (Level 2) [Member] | Treasuries, Other Debt [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		742	708
Significant Other Observable Inputs (Level 2) [Member] | Mortgage Backed Securities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		5	31
Significant Other Observable Inputs (Level 2) [Member] | Obligations Under Securities Lending [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		0	0
Significant Other Observable Inputs (Level 2) [Member] | Insurance Contracts [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		32	34
Significant Other Observable Inputs (Level 2) [Member] | Other [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total net assets		$ 0	$ 2

[1] Total net assets excludes non-financial plan receivables and payables of $25 million and $14 million, respectively, as of December 31, 2015 and $19 million and $26 million, respectively, as of December 31, 2014. 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, 2015 excludes investments in common/collective trusts, registered investment companies and short-term investment funds with fair values of $251 million, $117 million and $43 million, respectively. Total investments, at fair value, for the year ended December 31, 2014 excludes investments in common/collective trusts, registered investment companies and short-term investment funds with fair values of $278 million, $133 million and $263 million, respectively.