Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Restated			$ (55)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			(3)
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (49)	$ (52)
Other comprehensive income before reclassifications	(168)	(87)
Amounts reclassified from accumulated other comprehensive income	(78)	(81)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Income Tax Expense (Benefit)	(32)	(5)	(44)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	91	6
Ending Balance	42	(49)	(52)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	86	31
Other comprehensive income before reclassifications	(142)	(136)
Amounts reclassified from accumulated other comprehensive income	(76)	(81)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	65	55
Ending Balance	151	86	31
Accumulated Translation Adjustment [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(142)	(94)
Other comprehensive income before reclassifications	(26)	48
Amounts reclassified from accumulated other comprehensive income	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	26	(48)
Ending Balance	(116)	(142)	(94)
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			(3)
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2)	(3)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	1
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	1
Ending Balance	(2)	(2)	(3)
Other Postretirement Benefits Plan [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	9	11
Other comprehensive income before reclassifications	(1)	1
Amounts reclassified from accumulated other comprehensive income	(1)	(1)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(1)	(2)
Ending Balance	$ 8	$ 9	$ 11