Condensed Financial Information (Parent Company) (Condensed Statements of Operations) (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
Condensed Income Statements, Captions [Line Items]
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
Other expenses									13,150	13,689	13,714
Total expenses	19,254	15,092	13,902	12,667	17,180	15,887	15,200	14,558	60,915	62,825	61,634
Income (loss) before provision for income tax and equity in earnings of subsidiaries									6,927	6,795	6,307
Provision for income tax expense (benefit)									1,509	886	1,179
Equity in earnings of subsidiaries									829	795	592
Net income (loss)	158	706	145	4,398	593	2,184	1,741	1,381	5,407	5,899	5,123
Less: Preferred stock dividends	34	59	77	32	57	32	57	32	202	178	141
Preferred stock redemption premium	0	14	0	0					14	0	0
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 124	$ 633	$ 68	$ 4,366	$ 536	$ 2,152	$ 1,684	$ 1,349	5,191	5,721	4,982
Comprehensive income (loss)									10,427	17,208	(1,494)
Parent Company
Condensed Income Statements, Captions [Line Items]
Net investment income									50	77	87
Other revenues									29	27	19
Net investment gains (losses)									(154)	(40)	(277)
Net derivative gains (losses)									(61)	(45)	(56)
Total revenues									(136)	19	(227)
Expenses
Interest expense									833	850	1,009
Other expenses									154	153	158
Total expenses									987	1,003	1,167
Income (loss) before provision for income tax and equity in earnings of subsidiaries									(1,123)	(984)	(1,394)
Provision for income tax expense (benefit)									(267)	(582)	(51)
Equity in earnings of subsidiaries									6,263	6,301	6,466
Net income (loss)									5,407	5,899	5,123
Less: Preferred stock dividends									202	178	141
Preferred stock redemption premium									14	0	0
Net income (loss) available to MetLife, Inc.’s common shareholders									5,191	5,721	4,982
Comprehensive income (loss)									$ 10,427	$ 17,208	$ (1,494)