Defined Benefit Pension And Other Postretirement Plans (Fair Values Of Defined Benefit Pension Plan Assets) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	$ 2,089	$ 1,840
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	25	14
Equity investments, common stocks
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	175	36
Equity funds, mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	159	227
Equity funds, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	297	507
Fixed income, corporate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	860	674
Fixed income, government
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	239	98
Fixed income, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	201	176
Private equity
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	41	51
Real estate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	29	34
Other
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	63	23
Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	567	265
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 1 | Equity investments, common stocks
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	89	36
Level 1 | Equity funds, mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	159	227
Level 1 | Equity funds, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 1 | Fixed income, corporate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	176	0
Level 1 | Fixed income, government
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	98	0
Level 1 | Fixed income, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 1 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 1 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	45	2
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	1,434	1,470
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	25	14
Level 2 | Equity investments, common stocks
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	86	0
Level 2 | Equity funds, mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 2 | Equity funds, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	297	507
Level 2 | Fixed income, corporate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	684	673
Level 2 | Fixed income, government
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	141	98
Level 2 | Fixed income, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	201	176
Level 2 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 2 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	2
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	88	105	$ 118
Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 3 | Equity investments, common stocks
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 3 | Equity funds, mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 3 | Equity funds, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 3 | Fixed income, corporate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	1
Level 3 | Fixed income, government
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 3 | Fixed income, pooled funds
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	0	0
Level 3 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	41	51	60
Level 3 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	29	34	$ 39
Level 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Plan asset investments, at fair value	$ 18	$ 19