Identifiable Intangible Assets and Goodwill - Goodwill (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Goodwill [Roll Forward]
Balance, December 31, 2017	$ 55,952	[1]
Other	(338)	[2]
Balance, September 30, 2018	55,614	[1]
IH [Member]
Goodwill [Roll Forward]
Balance, December 31, 2017	31,141
Other	(178)	[2]
Balance, September 30, 2018	30,964
EH [Member]
Goodwill [Roll Forward]
Balance, December 31, 2017	24,811
Other	(160)	[2]
Balance, September 30, 2018	$ 24,651

[1] Amounts may not add due to rounding.

[2] Primarily reflects the impact of foreign exchange, as well as the contribution of the allogeneic CAR T developmental program assets and operations to Allogene that constituted a business for accounting purposes (see Note 2B).