SCHEDULE 13G

Amendment No. 2
MetLife Incorporated
Common Stock
Cusip #59156R108


Cusip #59156R108
Item 1:	Reporting Person - FMR LLC
Item 4:	Delaware
Item 5:	2,795,981
Item 6:	0
Item 7:	36,874,241
Item 8:	0
Item 9:	36,874,241
Item 11:	4.931%
Item 12:	    HC


Cusip #59156R108
Item 1:	Reporting Person - Edward C. Johnson 3d
Item 4:	United States of America
Item 5:	0
Item 6:	0
Item 7:	36,874,241
Item 8:	0
Item 9:	36,874,241
Item 11:	4.931%
Item 12:	IN




	SCHEDULE 13G - TO BE INCLUDED IN
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

This Amendment to Schedule 13G filed by FMR LLC amends
the statement on Schedule 13G previously filed by FMR
Corp., the predecessor of FMR LLC.


Item 1(a).	Name of Issuer:

		MetLife Incorporated

Item 1(b).	Name of Issuer's Principal Executive Offices:

		200 Park Avenue
		New York, NY  10166


Item 2(a).	Name of Person Filing:

		FMR LLC

Item 2(b).	Address or Principal Business Office or, if None,
Residence:

		82 Devonshire Street, Boston,
Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		Common Stock

Item 2(e).	CUSIP Number:

		59156R108

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-2(b)
and the person filing, FMR LLC, is a parent holding company
in accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See
Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	36,874,241

	(b)	Percent of Class:	4.931%

	(c)	Number of shares as to which such
person has:

	(i)	sole power to vote or to direct
the vote:	2,795,981

	(ii)	shared power to vote or to
direct the vote:	0

	(iii)	sole power to dispose or to
direct the disposition of:	36,874,241

	(iv)	shared power to dispose or to
direct the disposition of:	0



Item 5.	Ownership of Five Percent or Less of a Class.

	If this statement is being filed to report the fact that as of the
date hereof, the reporting person has ceased to be the
beneficial owner of more than five percent of the class of
securities, check the following (X).

Item 6.	Ownership of More than Five Percent on Behalf of Another
Person.

	Not applicable

Item 7.	Identification and Classification of the Subsidiary Which
Acquired the Security Being Reported on By the Parent
Holding Company.

	See attached Exhibit A.

Item 8.	Identification and Classification of Members of
the Group.

	Not applicable.  See attached Exhibit A.

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	Inasmuch as the reporting persons are no longer the beneficial
owners of more than five percent of the number of shares
outstanding, the reporting persons have no further reporting
obligation under Section 13(d) of the Securities and Exchange
Commission thereunder, and the reporting persons have no
obligation to amend this Statement if any material change
occurs in the facts set forth herein.

Signature

	After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this statement
is true, complete and correct.

February 13, 2008
Date

/s/Eric D. Roiter
Signature

Eric D. Roiter
Duly authorized under Power of Attorney
dated December 30, 1997 by and on behalf of FMR Corp.
(now known as FMR LLC) and its direct and indirect
subsidiaries



	SCHEDULE 13G - TO BE INCLUDED IN
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)



	Pursuant to the instructions in Item 7 of Schedule 13G,
Fidelity Management & Research Company ("Fidelity"), 82
Devonshire Street, Boston, Massachusetts 02109, a wholly-
owned subsidiary of FMR LLC and an investment adviser
registered under Section 203 of the Investment Advisers Act
of 1940, is the beneficial owner of 33,996,420 shares or
4.546% of the Common Stock outstanding of MetLife
Incorporated  ("the Company") as a result of acting as
investment adviser to various investment companies registered
under Section 8 of the Investment Company Act of 1940. The
number of shares of Common Stock of MetLife Incorporated
owned by the investment companies at December 31, 2007
included 7,172,400 shares of Common Stock resulting from
the assumed conversion of 7,172,400 shares of METLIFE INC
EQ UNIT (1 shares of Common Stock for each share of
Convertible Preferred Stock).

	Edward C. Johnson 3d and FMR LLC, through its
control of Fidelity, and the funds each has sole power to
dispose of the 33,996,420 shares owned by the Funds.

	Members of the family of Edward C. Johnson 3d,
Chairman of FMR LLC, are the predominant owners, directly
or through trusts, of Series B voting common shares of FMR
LLC, representing 49% of the voting power of FMR LLC.
The Johnson family group and all other Series B shareholders
have entered into a shareholders' voting agreement under
which all Series B voting common shares will be voted in
accordance with the majority vote of Series B voting common
shares.  Accordingly, through their ownership of voting
common shares and the execution of the shareholders' voting
agreement, members of the Johnson family may be deemed,
under the Investment Company Act of 1940, to form a
controlling group with respect to FMR LLC.

	Neither FMR LLC nor Edward C. Johnson 3d,
Chairman of FMR LLC, has the sole power to vote or direct
the voting of the shares owned directly by the Fidelity Funds,
which power resides with the Funds' Boards of Trustees.
Fidelity carries out the voting of the shares under written
guidelines established by the Funds' Boards of Trustees.

	Strategic Advisers, Inc., 82 Devonshire Street, Boston,
MA 02109, a wholly-owned subsidiary of FMR LLC and an
investment adviser registered under Section 203 of the
Investment Advisers Act of 1940, provides investment
advisory services to individuals.  As such, FMR LLC's
beneficial ownership includes 3,124 shares, or 0.000%, of the
Common Stock stock outstanding of MetLife Incorporated,
beneficially owned through Strategic Advisers, Inc.

	Pyramis Global Advisors, LLC ("PGALLC"), 53 State
Street, Boston, Massachusetts, 02109, an indirect wholly-
owned subsidiary of FMR LLC and an investment adviser
registered under Section 203 of the Investment Advisers Act
of 1940, is the beneficial owner of 821,200 shares or 0.110%
of the outstanding Common Stock of MetLife Incorporated as
a result of its serving as investment adviser to institutional
accounts, non-U.S. mutual funds, or investment companies
registered under Section 8 of the Investment Company Act of
1940 owning such shares. The number of shares of Common
Stock of MetLife Incorporated owned by the institutional
account(s) at December 31, 2007 included 371,100 shares of
Common Stock resulting from the assumed conversion of
371,100 shares of METLIFE INC EQ UNIT (1 shares of
Common Stock for each share of Convertible Preferred
Stock).

	Edward C. Johnson 3d and FMR LLC, through its
control of PGALLC, each has sole dispositive power over
821,200 shares and sole power to vote or to direct the voting
of 821,200 shares of Common Stock owned by the
institutional accounts or funds advised by PGALLC as
reported above.

	Pyramis Global Advisors Trust Company ("PGATC"),
53 State Street, Boston, Massachusetts, 02109, an indirect
wholly-owned subsidiary of FMR LLC and a bank as defined
in Section 3(a)(6) of the Securities Exchange Act of 1934, is
the beneficial owner of 1,110,382 shares or 0.148% of the
outstanding Common Stock of the MetLife Incorporated as a
result of its serving as investment manager of institutional
accounts owning such shares. The number of shares of
Common Stock of MetLife Incorporated owned by the
institutional account(s) at December 31, 2007 included
371,100 shares of Common Stock resulting from the assumed
conversion of 371,100 shares of METLIFE INC EQ UNIT (1
shares of Common Stock for each share of Convertible
Preferred Stock).

	Edward C. Johnson 3d and FMR LLC, through its
control of Pyramis Global Advisors Trust Company, each has
sole dispositive power over 1,110,382 shares and sole power
to vote or to direct the voting of 955,982 shares of Common
Stock owned by the institutional accounts managed by
PGATC as reported above.

	Fidelity International Limited ("FIL"), Pembroke Hall,
42 Crow Lane, Hamilton, Bermuda, and various foreign-based
subsidiaries provide investment advisory and management
services to a number of non-U.S. investment companies and
certain institutional investors.  FIL, which is a qualified
institution under section 240.13d-1(b)(1) pursuant to an SEC
No-Action letter dated October 5, 2000, is the beneficial
owner of 943,115 shares or 0.126% of the Common Stock
outstanding of the Company. The number of shares of
Common Stock of MetLife Incorporated owned by the
institutional account(s) at December 31, 2007 included
777,700 shares of Common Stock resulting from the assumed
conversion of 777,700 shares of METLIFE INC EQ UNIT (1
shares of Common Stock for each share of Convertible
Preferred Stock).

	Partnerships controlled predominantly by members of
the family of Edward C. Johnson 3d, Chairman of FMR LLC
and FIL, or trusts for their benefit, own shares of FIL voting
stock with the right to cast approximately 47% of the total
votes which may be cast by all holders of FIL voting stock.
FMR LLC and FIL are separate and independent corporate
entities, and their Boards of Directors are generally composed
of different individuals.

	FMR LLC and FIL are of the view that they are not
acting as a "group" for purposes of Section 13(d) under the
Securities Exchange Act of 1934 (the "1934" Act) and that
they are not otherwise required to attribute to each other the
"beneficial ownership" of securities "beneficially owned" by
the other corporation within the meaning of Rule 13d-3
promulgated under the 1934 Act.  Therefore, they are of the
view that the shares held by the other corporation need not be
aggregated for purposes of Section 13(d). However, FMR
LLC is making this filing on a voluntary basis as if all of the
shares are beneficially owned by FMR LLC and FIL on a joint
basis.

	FIL has sole dispositive power over 943,115 shares
owned by the International Funds. FIL has sole power to vote
or direct the voting of 905,115 shares and no power to vote or
direct the voting of 38,000 shares of Common Stock held by
the International Funds as reported above.


	SCHEDULE 13G - TO BE INCLUDED IN
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
	RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on February 13, 2008, agree
and consent to the joint filing on their behalf of this Schedule
13G in connection with their beneficial ownership of the
Common Stock of MetLife Incorporated at December 31,
2007.

	FMR LLC

	By /s/ Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney dated
December 30, 1997, by and on behalf of FMR Corp. (now
known as FMR LLC) and its direct and indirect subsidiaries

	Edward C. Johnson 3d

	By /s/ Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney dated
December 30, 1997, by and on behalf of Edward C. Johnson
3d

	Fidelity Management & Research Company

	By /s/ Eric D. Roiter
	Eric D. Roiter
	Senior V.P. and General Counsel