Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Benefit Plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan, net	100.00%
Cost of defined benefit plans	$ 499	$ 471	$ 444
Defined benefit plan cost	9	14	21
Defined benefit plan obligation	$ 68	118
Defined Contribution Benefit Plans [Member] | Minimum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	3.00%
Defined Contribution Benefit Plans [Member] | Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of employer contribution to match participant contribution in defined contribution plan	9.00%
Restoration Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Number of hours of service required to qualify for the plan	1,000 or more hours
Noncontributory and nonqualified plan, benefit expense	$ 22	40	20
Noncontributory and nonqualified plan, accrued benefits liabilities	205	201
Supplemental Executive Retirement Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan cost	26	28	$ 22
Defined benefit plan obligation	$ 195	$ 223