Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
U.S corporate income tax rate	35.00%	21.00%	35.00%
Non-cash increase in net income	$ 14	$ 6	$ 200
Increase in income tax benefit			268
Net deferred tax liabilities partially offset by provisional charge			78
Uncertain income tax positions	95
Reductions for tax positions related to a prior year	23	48	1
Additions for tax positions related to the current year	86	3	51
Net operating loss carryforwards	275	251
Uncertain tax position penalties	17	16
Uncertain tax position interest	4	3
Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	70
Net operating loss carryforwards indefinitely	$ 88
Net operating loss carryforwards expiration year	2034 and 2038
Foreign [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 2
Net operating loss carryforwards indefinitely	$ 77
Net operating loss carryforwards expiration year	2035 and 2039
Net operating loss carryforwards in foreign tax jurisdictions	$ 38
Tax credit carryforwards	$ 45
Tax credit carryforwards expiration year	2020 and 2030
Tax credit carryforwards indefinitely	$ 2
CNA Financial Corporation [Member]
Income Tax Contingency [Line Items]
Equity ownership percentage	80.00%
Diamond Offshore [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would affect effective tax rate upon recognition	$ 149	$ 82	$ 102