Benefit Plans (Fair Values of Pension and Postretirement Plan Assets) (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	$ 7,138,000,000	$ 8,015,000,000	$ 7,475,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	7,138,000,000	8,015,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	48,000,000	(1,000,000)
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,355,000,000	2,274,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Common stock: International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	237,000,000	1,396,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Common stock: U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,082,000,000	831,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	36,000,000	47,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	3,599,000,000	3,267,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	868,000,000	588,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	73,000,000	81,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	115,000,000	150,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,726,000,000	1,789,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	478,000,000	511,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Common stock: International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Common stock: U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	303,000,000	106,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	36,000,000	42,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Common stock: International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Common stock: U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	4,954,000,000	5,541,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	868,000,000	588,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	73,000,000	81,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	115,000,000	150,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,726,000,000	1,789,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	478,000,000	511,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Common stock: International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	237,000,000	1,396,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Common stock: U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,082,000,000	831,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	303,000,000	106,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	72,000,000	89,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	2,136,000,000	2,475,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member] | U S Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	1,722,000,000	2,014,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member] | U S Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	328,000,000	361,000,000
Pension [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member] | International Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	86,000,000	100,000,000
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	211,000,000	270,000,000	$ 0
Postretirement Benefit Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net		122,000,000
Postretirement Benefit Plan [Member] | Defined Benefit Plan, Common Collective Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net		148,000,000
Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0	0
Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net		$ 0
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	211,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	9,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	2,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	0
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	2,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	97,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	13,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	3,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	71,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	8,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	2,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	99,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	13,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	3,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Corporate Debt Security, Above Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	71,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Corporate Debt Security, Below Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	8,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Other, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	4,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	103,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member] | U S Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	77,000,000
Postretirement Benefit Plan [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member] | International Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, net	$ 26,000,000