Benefit Plans (Fair Values of Pension Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	$ 7,475	$ 6,706
U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	444	331
U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	102	102
U.S. And Foreign Government Securities Or Their Agencies [Member] | Foreign government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	185	252
Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,735	1,660
Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	602	502
Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,076	909
Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	760	605
Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	51	58
Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	137	87
Plan Asset Categories, Excluding Investments Measured at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	5,092	4,506
Common/Collective Trusts [Member] | U.S. large cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,940	1,762
Common/Collective Trusts [Member] | U.S. small cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	363	360
Common/Collective Trusts [Member] | International developed markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	80	78
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]
Fair value of plan assets, net	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]
Fair value of plan assets, net	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]
Fair value of plan assets, net	0	0
Level 1 [Member] | Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 1 [Member] | Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 1 [Member] | Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,076	907
Level 1 [Member] | Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	760	605
Level 1 [Member] | Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	51	58
Level 1 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	91	16
Level 1 [Member] | Plan Asset Categories, Excluding Investments Measured at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,978	1,586
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]
Fair value of plan assets, net	444	331
Level 2 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | U.S. municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	102	102
Level 2 [Member] | U.S. And Foreign Government Securities Or Their Agencies [Member] | Foreign government and agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	185	252
Level 2 [Member] | Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,735	1,660
Level 2 [Member] | Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	602	502
Level 2 [Member] | Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 2 [Member] | Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 2 [Member] | Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 2 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	33	58
Level 2 [Member] | Plan Asset Categories, Excluding Investments Measured at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	3,101	2,905
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]
Fair value of plan assets, net	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]
Fair value of plan assets, net	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]
Fair value of plan assets, net	0	0
Level 3 [Member] | Corporate Debt Instruments [Member] | Above investment grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 3 [Member] | Corporate Debt Instruments [Member] | Below grade investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 3 [Member] | Common Stock [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	2
Level 3 [Member] | Common Stock [Member] | U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 3 [Member] | Registered Investment Companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Level 3 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	13	13
Level 3 [Member] | Plan Asset Categories, Excluding Investments Measured at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	$ 13	$ 15