SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Summary of Signficant Accounting Policies - Additional Information (Detail) $ in Millions, ¥ in Billions		1 Months Ended	12 Months Ended
		Nov. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) series	Dec. 31, 2018 USD ($)	Dec. 31, 2020 JPY (¥)	Apr. 30, 2020 USD ($)	Mar. 31, 2020 JPY (¥) series	Jan. 01, 2020 USD ($)	Dec. 31, 2019 JPY (¥) series	Nov. 30, 2019 USD ($)	Jan. 01, 2019 USD ($)	Oct. 31, 2018 JPY (¥) series	Dec. 31, 2017 USD ($)	Sep. 30, 2016 USD ($) series
Significant Accounting Policies [Line Items]
Contingent Consideration Payment			$ 14
Number of series of senior notes issued through a U.S. public debt offering (in series) | series				4				4		4			3		2
Goodwill			269	$ 140
Stockholders' Equity Attributable to Parent			33,559	$ 28,959	$ 23,462									$ 24,598
Zurich North America's U.S. Corporate Life and Pensions business
Significant Accounting Policies [Line Items]
Payments to Acquire Businesses, Gross		$ 140
Argus Dental & Vision, Inc. [Member]
Significant Accounting Policies [Line Items]
Payments to Acquire Businesses, Gross		$ 75
Federal Home Loan Bank of Atlanta [Member]
Significant Accounting Policies [Line Items]
Line of credit facility, maximum borrowing capacity							$ 800
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases							300
100.0 billion yen line of credit
Significant Accounting Policies [Line Items]
Line of credit facility, maximum borrowing capacity | ¥						¥ 100.0
$1.0 billion line of credit
Significant Accounting Policies [Line Items]
Line of credit facility, maximum borrowing capacity			$ 1,000
Senior Notes
Significant Accounting Policies [Line Items]
Debt Instrument, Face Amount								¥ 57.0		¥ 38.0			¥ 53.4		$ 700
3.60% senior notes due April 2030
Significant Accounting Policies [Line Items]
Debt Instrument, Face Amount							$ 1,000
Maximum
Significant Accounting Policies [Line Items]
Business Combination, Contingent Consideration, Liability											$ 21
Aflac Japan
Significant Accounting Policies [Line Items]
Percentage of the Company's total revenues			68.00%	69.00%	70.00%
Percentage of the Company's total assets			83.00%	83.00%		83.00%				83.00%
Accounting Standards Update 2016-01 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[1]													0
Accounting Standards Update 2018-02 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[1]													0
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle, cumulative effect of change on assets												$ 134
New accounting pronouncement or change in accounting principle, cumulative effect of change on liabilities												$ 134
Accounting Standards Update 2019-04
Significant Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle effect of adoption reclassification from held to maturity to available for sale debt securities									$ 6,900
New accounting pronouncement or change in accounting principle effect of adoption unrealized gain loss net of tax reclassification to accumulated other comprehensive income									$ 848
Accounting Standards Update 2019-04 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[2]			$ 848
Accounting Standards Update 2016-13 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[2]			(56)
Accumulated other comprehensive income (loss)
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent			$ 8,934	6,615	$ 2,151									4,028
Accumulated other comprehensive income (loss) | Accounting Standards Update 2016-01 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[1]													(148)
Accumulated other comprehensive income (loss) | Accounting Standards Update 2018-02 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[1]													374
Accumulated other comprehensive income (loss) | Accounting Standards Update 2019-04 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[2]			848
Accumulated other comprehensive income (loss) | Accounting Standards Update 2016-13 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[2]			0
Retained earnings
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent			$ 37,984	34,291	$ 31,788									29,895
Retained earnings | Accounting Standards Update 2016-01 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[1]													148
Retained earnings | Accounting Standards Update 2018-02 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[1]													$ (374)
Retained earnings | Accounting Standards Update 2019-04 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[2]			0
Retained earnings | Accounting Standards Update 2016-13 | Cumulative effect, period of adoption, adjustment
Significant Accounting Policies [Line Items]
Stockholders' Equity Attributable to Parent	[2]			$ (56)

[1] See Note 1 of the Notes to the Consolidated Financial Statements for the adoption of accounting guidance on January 1, 2018.

[2] See Note 1 of the Notes to the Consolidated Financial Statements for the adoption of accounting guidance on January 1, 2020.