Business, Basis of Presentation and Summary of Significant Accounting Policies - Transition Table - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums, reinsurance and other receivables	$ 19,002		$ 17,364				$ 18,169
Market risk benefits	334		280
Deferred policy acquisition costs and value of business acquired	19,737		19,653	$ 18,546			20,417
Deferred income tax asset	3,174		2,439
Other assets	10,862		11,025				11,742
Total Assets	652,120		663,072
Future policy benefits	181,755		187,222				224,358
Policyholder Account Balance	213,933		210,597				211,737
Market risk benefits	2,738		3,763				7,901
Other Policy-Related Balances	19,665		18,424				18,032
Deferred income tax liability	128		950				4,723
Other liabilities	34,698		25,933
Total Liabilities	626,225		632,947
Retained earnings	39,958		40,332				31,824
Accumulated other comprehensive income (loss)	(24,254)	$ (20,386)	(22,621)	(22,526)	$ (18,106)	$ (2,451)	$ 315
Total MetLife, Inc.’s stockholders’ equity	25,658		29,881
Noncontrolling interests	237		244
Total equity	25,895	$ 30,492	30,125	29,640	34,009	50,013
Total liabilities and equity	$ 652,120		663,072
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums, reinsurance and other receivables			17,461					$ 17,870
Market risk benefits			0
Deferred policy acquisition costs and value of business acquired			22,983					16,389
Deferred income tax asset			2,830
Other assets			11,026					11,685
Total Assets			666,611
Future policy benefits			204,228					206,656
Policyholder Account Balance			203,082					205,176
Market risk benefits			0					0
Other Policy-Related Balances			19,651					17,101
Deferred income tax liability			325					11,008
Other liabilities			25,980
Total Liabilities			639,324
Retained earnings			41,953					36,491
Accumulated other comprehensive income (loss)			(27,083)					$ 18,072
Total MetLife, Inc.’s stockholders’ equity			27,040
Noncontrolling interests			247
Total equity			27,287	$ 25,330	$ 37,367	$ 67,749
Total liabilities and equity			666,611
Revision of Prior Period, Accounting Standards Update, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums, reinsurance and other receivables			(97)
Market risk benefits			280
Deferred policy acquisition costs and value of business acquired			(3,330)
Deferred income tax asset			(391)
Other assets			(1)
Total Assets			(3,539)
Future policy benefits			(17,006)
Policyholder Account Balance			7,515
Market risk benefits			3,763
Other Policy-Related Balances			(1,227)
Deferred income tax liability			625
Other liabilities			(47)
Total Liabilities			(6,377)
Retained earnings			(1,621)
Accumulated other comprehensive income (loss)			4,462
Total MetLife, Inc.’s stockholders’ equity			2,841
Noncontrolling interests			(3)
Total equity			2,838
Total liabilities and equity			$ (3,539)