Benefit Plans (Fair Value of Pension Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016		Dec. 31, 2015
U S And International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	60.00%		61.00%
U S And International Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	19.00%		18.00%
Real Estate And Other Money Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	11.00%		11.00%
Investment Funds Holding Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	10.00%		10.00%
Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 4,420		$ 4,513
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	1,740		1,593
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	0		0
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	6,160		6,106
Investment funds measured at net asset value	297	[1]	298	[2]
Total assets	6,457		6,404
Pension [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	8		225
Pension [Member] | Equity securities [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	131		120
Pension [Member] | Equity securities [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	432		409
Pension [Member] | Investment funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	5,270	[3]	5,039
Pension [Member] | International government bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	309		289
Pension [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	10		24
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	4,420		4,513
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	8		225
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member] | Equity securities [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	131		120
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member] | Equity securities [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	432		409
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member] | Investment funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	3,530	[3]	3,446	[4]
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member] | International government bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	309		289
Pension [Member] | Quoted Prices In Active Markets For Identical Assets/Liabilities (Level 1) [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	10		24
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	1,740		1,593
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member] | Equity securities [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member] | Equity securities [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member] | Investment funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	1,740	[3]	1,593	[4]
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member] | International government bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	0		0
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity securities [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity securities [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member] | Investment funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets		[3]		[4]
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member] | International government bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets

[1] In accordance with FASB ASC Subtopic 820-10, certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position.

[2] In accordance with FASB ASC Subtopic 820-10, certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the statement of financial position.

[3] Investment funds whose objective seeks to replicate the returns and characteristics of specified market indices (primarily MSCI — Europe, Switzerland, North America, Asia Pacific, Japan; Russell 3000; S&P 500 for equities, and Citigroup EMU and Barclays Capital U.S. for bonds), primarily consist of mutual funds, common trust funds and commingled funds. Of these funds, 60% are invested in U.S. and international equities; 19% are invested in U.S. and international government bonds; 11% are invested in real estate and other money markets, and 10% are invested in corporate bonds.

[4] Investment funds whose objective seeks to replicate the returns and characteristics of specified market indices (primarily MSCI — Europe, Switzerland, North America, Asia Pacific, Japan; Russell 3000; S&P 500 for equities, and Citigroup EMU and Barclays Capital U.S. for bonds), primarily consist of mutual funds, common trust funds and commingled funds. Of these funds, 61% were invested in U.S. and international equities; 18% were invested in U.S. and international government bonds; 11% were invested in real estate and other money markets, and 10% were invested in corporate bonds.