Accumulated Other Comprehensive Loss - Changes (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI roll forward
Beginning balance	$ 7,354	$ 6,893	$ 7,454	$ 7,070
Other comprehensive income (loss), net of tax	(58)	25	(27)	(8)
Ending balance	7,174	7,157	7,174	7,157
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI roll forward
Beginning balance	70	(41)	39	(8)
Other comprehensive income (loss) before reclassifications, net of tax (expense) benefit			1
Amounts reclassified from accumulated other comprehensive (income) loss, net of tax (expense) benefit			(28)
Other comprehensive income (loss), net of tax	(58)	25	(27)	(8)
Ending balance	12	$ (16)	12	$ (16)
Derivative Instruments [Member]
AOCI roll forward
Beginning balance			(9)
Amounts reclassified from accumulated other comprehensive (income) loss, net of tax (expense) benefit			8
Other comprehensive income (loss), net of tax			8
Ending balance	(1)		(1)
Available-for-Sale Debt Securities [Member]
AOCI roll forward
Beginning balance			49
Other comprehensive income (loss) before reclassifications, net of tax (expense) benefit			(3)
Other comprehensive income (loss), net of tax			(3)
Ending balance	46		46
Foreign Currency Translation Adjustments [Member]
AOCI roll forward
Beginning balance			(1)
Other comprehensive income (loss) before reclassifications, net of tax (expense) benefit			4
Amounts reclassified from accumulated other comprehensive (income) loss, net of tax (expense) benefit	35		(35)
Other comprehensive income (loss), net of tax			(31)
Ending balance	(32)		(32)
Post - Retirement Benefit Obligation [Member]
AOCI roll forward
Amounts reclassified from accumulated other comprehensive (income) loss, net of tax (expense) benefit			(1)
Other comprehensive income (loss), net of tax			(1)
Ending balance	$ (1)		$ (1)