Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Weighted Average Shares:
Weighted average common stock outstanding - basic									907.8	937.6	1,005.9
Incremental common shares from assumed exercise or issuance of stock-based awards									5.4	6.8	8.0
Weighted average common stock outstanding - diluted									913.2	944.4	1,013.9
Net Income (Loss):
Net income (loss)	$ 158	$ 709	$ 150	$ 4,401	$ 588	$ 2,190	$ 1,746	$ 1,385	$ 5,418	$ 5,909	$ 5,128
Less: Net income (loss) attributable to noncontrolling interests	0	3	5	3	(5)	6	5	4	11	10	5
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
Basic	$ 0.14	$ 0.70	$ 0.07	$ 4.78	$ 0.58	$ 2.31	$ 1.78	$ 1.41	$ 5.72	$ 6.10	$ 4.95
Diluted	$ 0.14	$ 0.69	$ 0.07	$ 4.75	$ 0.58	$ 2.30	$ 1.77	$ 1.40	$ 5.68	$ 6.06	$ 4.91