Note 4. Investments in fixed maturity securities

Our investments in fixed maturity securities as of September 30, 2018 and December 31, 2017 are summarized by type below (in millions).


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
September 30, 2018
U.S. Treasury, U.S. government corporations and agencies	$	3,626	$	8	$	(35)	$	3,599
U.S. states, municipalities and political subdivisions		276		15		(1)		290
Foreign governments		7,362		45		(37)		7,370
Corporate bonds		6,029		436		(7)		6,458
Mortgage-backed securities		502		56		(4)		554

	$	17,795	$	560	$	(84)	$	18,271

December 31, 2017
U.S. Treasury, U.S. government corporations and agencies	$	3,975	$	4	$	(26)	$	3,953
U.S. states, municipalities and political subdivisions		847		19		(12)		854
Foreign governments		8,572		274		(24)		8,822
Corporate bonds		6,279		588		(5)		6,862
Mortgage-backed securities		772		92		(2)		862

	$	20,445	$	977	$	(69)	$	21,353

Investments in foreign government securities include securities issued by national and provincial government entities as well as instruments that are unconditionally guaranteed by such entities. As of September 30, 2018, approximately 89% of foreign government holdings were rated AA or higher by at least one of the major rating agencies.

The amortized cost and estimated fair value of fixed maturity securities at September 30, 2018 are summarized below by contractual maturity dates. Amounts are in millions. Actual maturities may differ from contractual maturities due to early call or prepayment rights held by issuers.


	Due in one year or less		Due after one year through five years		Due after five years through ten years		Due after ten years		Mortgage- backed securities		Total
Amortized cost	$	7,275	$	9,057	$	387	$	574	$	502	$	17,795
Fair value		7,274		9,108		435		900		554		18,271