Benefit Plans (Fair Values of Pension Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	$ 6,706	$ 7,297
Common/Collective Trusts [Member] | U.S. large cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	1,762	1,870
Common/Collective Trusts [Member] | U.S. small cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	360	442
Common/Collective Trusts [Member] | International developed markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	78	79
U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	331	296
U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	102	124
U.S. And Foreign Government Securities Or Their Agencies [Member] | Foreign government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	252	281
Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	1,660	1,765
Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	502	527
Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	909	1,001
Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	605	556
Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	58	176
Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	87	180
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	1,586	1,693
Level 1 [Member] | Common/Collective Trusts [Member] | U.S. large cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | Common/Collective Trusts [Member] | U.S. small cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | Common/Collective Trusts [Member] | International developed markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | Foreign government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 1 [Member] | Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	907	1,000
Level 1 [Member] | Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	605	556
Level 1 [Member] | Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	58	63
Level 1 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	16	74
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	5,105	5,588
Level 2 [Member] | Common/Collective Trusts [Member] | U.S. large cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	1,762	1,870
Level 2 [Member] | Common/Collective Trusts [Member] | U.S. small cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	360	442
Level 2 [Member] | Common/Collective Trusts [Member] | International developed markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	78	79
Level 2 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	331	296
Level 2 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	102	124
Level 2 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | Foreign government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	252	281
Level 2 [Member] | Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	1,660	1,765
Level 2 [Member] | Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	502	527
Level 2 [Member] | Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 2 [Member] | Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 2 [Member] | Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	113
Level 2 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	58	91
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	15	16
Level 3 [Member] | Common/Collective Trusts [Member] | U.S. large cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Common/Collective Trusts [Member] | U.S. small cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Common/Collective Trusts [Member] | International developed markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | Foreign government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	2	1
Level 3 [Member] | Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	0	0
Level 3 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments at fair value	$ 13	$ 15