Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 42	$ (49)
Other comprehensive income before reclassifications	(58)	(168)
Amounts reclassified from accumulated other comprehensive income	(21)	(78)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ 0
Income Tax Expense (Benefit)	3	(32)	(5)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	37	91
Ending Balance	79	42	(49)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	151	86
Other comprehensive income before reclassifications	(36)	(142)
Amounts reclassified from accumulated other comprehensive income	(21)	(76)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	15	65
Ending Balance	166	151	86
Accumulated Translation Adjustment [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(116)	(142)
Other comprehensive income before reclassifications	(23)	(26)
Amounts reclassified from accumulated other comprehensive income	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	23	26
Ending Balance	(92)	(116)	(142)
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2)	(2)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	1	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	1	0
Ending Balance	0	(2)	(2)
Other Postretirement Benefits Plan [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	8	9
Other comprehensive income before reclassifications	2	(1)
Amounts reclassified from accumulated other comprehensive income	(1)	(1)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(3)	(1)
Ending Balance	$ 5	$ 8	$ 9