Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan Termination Reclass of Deferred Losses from AOCI into Net Income				$ 61
Performance Stock Units Expense	[1]	$ 10	$ 17	36	$ 57
Restricted Stock or Unit Expense		21	14	82	64
Share-based Compensation		$ 31	$ 31	$ 118	$ 121

[1] Phantom stock units are settled in cash. During the three and nine months ended September 30, 2018, the Company paid $1 million and $76 million, respectively, related to these share-based liabilities. During the three and nine months ended September 30, 2017, the Company paid $2 million and $79 million, respectively, related to these share-based liabilities.