Segment Information (Earnings) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Premiums									$ 42,034	$ 42,235	$ 43,840
Universal life and investment-type product policy fees									5,603	5,603	5,502
Net investment income									17,117	18,868	16,166
Other revenues									1,849	1,842	1,880
Net investment gains (losses)									(110)	444	(298)
Net derivative gains (losses)									1,349	628	851
Total revenues	$ 19,418	$ 16,015	$ 14,099	$ 18,310	$ 17,143	$ 18,678	$ 17,497	$ 16,302	67,842	69,620	67,941
Expenses
Policyholder benefits and claims and policyholder dividends									42,551	42,672	43,907
Interest credited to policyholder account balances									5,214	6,464	4,013
Capitalization of DAC									(3,013)	(3,358)	(3,254)
Amortization of DAC and VOBA									3,160	2,896	2,975
Amortization of negative VOBA									(45)	(33)	(56)
Interest expense on debt									913	955	1,122
Other expenses									12,135	13,229	12,927
Total expenses	$ 19,254	$ 15,092	$ 13,902	$ 12,667	$ 17,180	$ 15,887	$ 15,200	$ 14,558	60,915	62,825	61,634
Provision for income tax expense (benefit)									1,509	886	1,179
Net income (loss)									5,418	5,909	5,128
U.S.
Expenses
Amortization of DAC and VOBA									471	475	477
Asia
Expenses
Amortization of DAC and VOBA									1,468	1,380	1,297
Latin America
Expenses
Amortization of DAC and VOBA									276	291	209
EMEA
Expenses
Amortization of DAC and VOBA									452	420	433
MetLife Holdings
Expenses
Amortization of DAC and VOBA									485	324	553
Corporate & Other
Expenses
Amortization of DAC and VOBA									8	6	6
Operating Segments
Revenues
Premiums									41,982	42,164	43,840
Universal life and investment-type product policy fees									5,465	5,395	5,382
Net investment income									17,328	17,830	17,383
Other revenues									1,690	1,585	1,556
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									66,465	66,974	68,161
Expenses
Policyholder benefits and claims and policyholder dividends									41,859	42,192	43,733
Interest credited to policyholder account balances									4,673	5,029	4,693
Capitalization of DAC									(3,008)	(3,338)	(3,253)
Amortization of DAC and VOBA									2,994	2,787	2,760
Amortization of negative VOBA									(45)	(33)	(55)
Interest expense on debt									913	955	1,059
Other expenses									11,872	12,778	12,529
Total expenses									59,258	60,370	61,466
Provision for income tax expense (benefit)									1,382	659	1,093
Adjusted earnings									5,825	5,945	5,602
Operating Segments | U.S.
Revenues
Premiums									27,265	26,801	28,186
Universal life and investment-type product policy fees									1,070	1,078	1,053
Net investment income									6,903	7,021	6,977
Other revenues									957	887	821
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									36,195	35,787	37,037
Expenses
Policyholder benefits and claims and policyholder dividends									26,309	26,165	27,765
Interest credited to policyholder account balances									1,622	1,984	1,790
Capitalization of DAC									(453)	(484)	(449)
Amortization of DAC and VOBA									471	475	477
Amortization of negative VOBA									0	0	0
Interest expense on debt									7	10	12
Other expenses									4,162	4,075	3,902
Total expenses									32,118	32,225	33,497
Provision for income tax expense (benefit)									853	724	736
Adjusted earnings									3,224	2,838	2,804
Operating Segments | Asia
Revenues
Premiums									6,571	6,632	6,766
Universal life and investment-type product policy fees									1,892	1,674	1,630
Net investment income									3,938	3,691	3,317
Other revenues									61	56	51
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									12,462	12,053	11,764
Expenses
Policyholder benefits and claims and policyholder dividends									5,213	5,185	5,326
Interest credited to policyholder account balances									1,834	1,710	1,465
Capitalization of DAC									(1,652)	(1,913)	(1,915)
Amortization of DAC and VOBA									1,415	1,288	1,302
Amortization of negative VOBA									(37)	(25)	(39)
Interest expense on debt									0	0	0
Other expenses									3,481	3,818	3,840
Total expenses									10,254	10,063	9,979
Provision for income tax expense (benefit)									643	585	548
Adjusted earnings									1,565	1,405	1,237
Operating Segments | Latin America
Revenues
Premiums									2,265	2,723	2,760
Universal life and investment-type product policy fees									994	1,094	1,050
Net investment income									992	1,271	1,239
Other revenues									38	44	35
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									4,289	5,132	5,084
Expenses
Policyholder benefits and claims and policyholder dividends									2,406	2,623	2,602
Interest credited to policyholder account balances									240	332	394
Capitalization of DAC									(362)	(396)	(377)
Amortization of DAC and VOBA									276	291	209
Amortization of negative VOBA									0	0	(1)
Interest expense on debt									4	3	6
Other expenses									1,318	1,443	1,421
Total expenses									3,882	4,296	4,254
Provision for income tax expense (benefit)									127	227	238
Adjusted earnings									280	609	592
Operating Segments | EMEA
Revenues
Premiums									2,259	2,177	2,131
Universal life and investment-type product policy fees									433	423	431
Net investment income									269	291	293
Other revenues									52	54	66
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									3,013	2,945	2,921
Expenses
Policyholder benefits and claims and policyholder dividends									1,196	1,176	1,127
Interest credited to policyholder account balances									109	98	100
Capitalization of DAC									(491)	(505)	(468)
Amortization of DAC and VOBA									454	428	434
Amortization of negative VOBA									(8)	(8)	(15)
Interest expense on debt									1	0	0
Other expenses									1,344	1,399	1,378
Total expenses									2,605	2,588	2,556
Provision for income tax expense (benefit)									81	75	88
Adjusted earnings									327	282	277
Operating Segments | MetLife Holdings
Revenues
Premiums									3,600	3,748	3,879
Universal life and investment-type product policy fees									1,073	1,124	1,218
Net investment income									5,184	5,281	5,379
Other revenues									238	253	250
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									10,095	10,406	10,726
Expenses
Policyholder benefits and claims and policyholder dividends									6,738	6,970	6,833
Interest credited to policyholder account balances									868	905	944
Capitalization of DAC									(39)	(28)	(36)
Amortization of DAC and VOBA									370	299	332
Amortization of negative VOBA									0	0	0
Interest expense on debt									6	8	9
Other expenses									942	969	1,081
Total expenses									8,885	9,123	9,163
Provision for income tax expense (benefit)									234	249	308
Adjusted earnings									976	1,034	1,255
Operating Segments | Corporate & Other
Revenues
Premiums									22	83	118
Universal life and investment-type product policy fees									3	2	0
Net investment income									42	275	178
Other revenues									344	291	333
Net investment gains (losses)									0	0	0
Net derivative gains (losses)									0	0	0
Total revenues									411	651	629
Expenses
Policyholder benefits and claims and policyholder dividends									(3)	73	80
Interest credited to policyholder account balances									0	0	0
Capitalization of DAC									(11)	(12)	(8)
Amortization of DAC and VOBA									8	6	6
Amortization of negative VOBA									0	0	0
Interest expense on debt									895	934	1,032
Other expenses									625	1,074	907
Total expenses									1,514	2,075	2,017
Provision for income tax expense (benefit)									(556)	(1,201)	(825)
Adjusted earnings									(547)	(223)	(563)
Significant Reconciling Items
Revenues
Premiums									52	71	0
Universal life and investment-type product policy fees									138	208	120
Net investment income									(211)	1,038	(1,217)
Other revenues									159	257	324
Net investment gains (losses)									(110)	444	(298)
Net derivative gains (losses)									1,349	628	851
Total revenues									1,377	2,646	(220)
Expenses
Policyholder benefits and claims and policyholder dividends									692	480	174
Interest credited to policyholder account balances									541	1,435	(680)
Capitalization of DAC									(5)	(20)	(1)
Amortization of DAC and VOBA									166	109	215
Amortization of negative VOBA									0	0	(1)
Interest expense on debt									0	0	63
Other expenses									263	451	398
Total expenses									1,657	2,455	168
Provision for income tax expense (benefit)									$ 127	$ 227	$ 86