Business, Basis of Presentation and Summary of Significant Accounting Policies - Transition Table - Income Statement (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums									$ 44,283	$ 48,510	$ 41,152
Universal life and investment-type product policy fees									5,152	5,225	5,244
Other revenues									2,526	2,630	2,619
Net investment gains (losses)									(2,824)	(1,260)	1,543
Net derivative gains (losses)									(2,140)	(2,251)	(3,257)
Total revenues	$ 19,028	$ 15,866	$ 16,623	$ 15,388	$ 15,608	$ 22,283	$ 15,474	$ 15,405	66,905	68,770	68,696
Policyholder benefits and claims									44,590	49,507	43,118
Policyholder liability remeasurement (gains) losses									(45)	114	(172)
Market Risk Benefit Remeasurement (Gains) Losses									(994)	(3,674)	(1,237)
Interest credited to policyholder account balances									7,860	3,894	5,571
Policyholder dividends									622	706	880
Other expenses									12,710	11,859	12,018
Total expenses	18,087	15,332	16,193	15,131	13,582	20,868	14,486	13,470	64,743	62,406	60,178
Income (loss) before provision for income tax									2,162	6,364	8,518
Provision for income tax expense (benefit)									560	1,062	1,642
Net income (loss)	614	495	408	85	1,581	1,167	915	1,639	1,602	5,302	6,876
Net Income (Loss) Attributable to Noncontrolling Interest	7	6	6	5	3	5	5	5	24	18	21
Net income (loss) attributable to MetLife, Inc.	607	489	402	80	1,578	1,162	910	1,634	1,578	5,284	6,855
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 574	$ 422	$ 370	$ 14	$ 1,549	$ 1,098	$ 881	$ 1,571	$ 1,380	$ 5,099	$ 6,654
Basic	$ 0.78	$ 0.56	$ 0.48	$ 0.02	$ 1.98	$ 1.38	$ 1.09	$ 1.91	$ 1.82	$ 6.35	$ 7.71
Diluted	$ 0.77	$ 0.56	$ 0.48	$ 0.02	$ 1.96	$ 1.37	$ 1.08	$ 1.89	$ 1.81	$ 6.30	$ 7.65
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums										$ 49,397	$ 42,009
Universal life and investment-type product policy fees										5,585	5,756
Other revenues										2,634	2,619
Net investment gains (losses)										(1,262)	1,529
Net derivative gains (losses)										(2,372)	(2,228)
Total revenues										69,898	71,080
Policyholder benefits and claims										50,612	43,954
Policyholder liability remeasurement (gains) losses										0	0
Market Risk Benefit Remeasurement (Gains) Losses										0	0
Interest credited to policyholder account balances										3,692	5,538
Policyholder dividends										701	876
Other expenses										12,034	12,586
Total expenses										67,039	62,954
Income (loss) before provision for income tax										2,859	8,126
Provision for income tax expense (benefit)										301	1,551
Net income (loss)										2,558	6,575
Net Income (Loss) Attributable to Noncontrolling Interest										19	21
Net income (loss) attributable to MetLife, Inc.										2,539	6,554
Net income (loss) available to MetLife, Inc.’s common shareholders										$ 2,354	$ 6,353
Basic										$ 2.93	$ 7.36
Diluted										$ 2.91	$ 7.31
Revision of Prior Period, Accounting Standards Update, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums										$ (887)	$ (857)
Universal life and investment-type product policy fees										(360)	(512)
Other revenues										(4)	0
Net investment gains (losses)										2	14
Net derivative gains (losses)										121	(1,029)
Total revenues										(1,128)	(2,384)
Policyholder benefits and claims										(1,105)	(836)
Policyholder liability remeasurement (gains) losses										114	(172)
Market Risk Benefit Remeasurement (Gains) Losses										(3,674)	(1,237)
Interest credited to policyholder account balances										202	33
Policyholder dividends										5	4
Other expenses										(175)	(568)
Total expenses										(4,633)	(2,776)
Income (loss) before provision for income tax										3,505	392
Provision for income tax expense (benefit)										761	91
Net income (loss)										2,744	301
Net Income (Loss) Attributable to Noncontrolling Interest										(1)	0
Net income (loss) attributable to MetLife, Inc.										2,745	301
Net income (loss) available to MetLife, Inc.’s common shareholders										$ 2,745	$ 301
Basic										$ 3.42	$ 0.35
Diluted										$ 3.39	$ 0.34