Employee Benefit Plans (Fair Values of the Company's Pension Plan Assets by Asset Category) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	$ 2,618	$ 2,883
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	1,961	2,056
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	252	212
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	914	842
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	795	1,002	$ 515
Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	657	827
Defined Benefit Plan, Equity Securities, US, Large Cap | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	137	83
Defined Benefit Plan, Equity Securities, US, Large Cap | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	43	0
Defined Benefit Plan, Equity Securities, US, Large Cap | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	94	83
Defined Benefit Plan, Equity Securities, US, Large Cap | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Defined Benefit Plan, Equity Securities, US, Small Cap | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	23	29
Defined Benefit Plan, Equity Securities, US, Small Cap | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	23	29
Defined Benefit Plan, Equity Securities, US, Small Cap | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Defined Benefit Plan, Equity Securities, US, Small Cap | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Defined Benefit Plan, Equity Securities, Non-US | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	218	194
Defined Benefit Plan, Equity Securities, Non-US | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	115	115
Defined Benefit Plan, Equity Securities, Non-US | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	103	79
Defined Benefit Plan, Equity Securities, Non-US | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Defined Benefit Plan, Cash and Cash Equivalents | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	22	11
Defined Benefit Plan, Cash and Cash Equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	3	0
Defined Benefit Plan, Cash and Cash Equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	19	11
Defined Benefit Plan, Cash and Cash Equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Debt Security, Corporate, US | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	297	287
Debt Security, Corporate, US | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Debt Security, Corporate, US | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	220	201
Debt Security, Corporate, US | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	77	86
Debt Security, Developed Markets And Emerging Economies | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	4	43
Debt Security, Developed Markets And Emerging Economies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Debt Security, Developed Markets And Emerging Economies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	4	43
Debt Security, Developed Markets And Emerging Economies | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Debt Security, Diverse Portfolio | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	142	124
Debt Security, Diverse Portfolio | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Debt Security, Diverse Portfolio | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	142	124
Debt Security, Diverse Portfolio | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
US Government Agencies Debt Securities | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	76	69
US Government Agencies Debt Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	68	68
US Government Agencies Debt Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	8	1
US Government Agencies Debt Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Developed Markets, Government Agencies Debt Securities | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	6	101
Developed Markets, Government Agencies Debt Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Developed Markets, Government Agencies Debt Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	6	101
Developed Markets, Government Agencies Debt Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Other | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	373	432
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	14	14
Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	359	418
Defined Benefit Plan, Real Estate, Hedge Funds, And Other [Member] | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	663	683
Defined Benefit Plan, Real Estate, Hedge Funds, And Other [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	0	0
Defined Benefit Plan, Real Estate, Hedge Funds, And Other [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	304	185
Defined Benefit Plan, Real Estate, Hedge Funds, And Other [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	$ 359	$ 498