Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Less than one year	$ 1,017
One year through five years	5,378
After five years through ten years	3,098
Greater than ten years	3,693
Amortized Cost	15,708	$ 15,119
Fair Value
Less than one year	1,022
One year through five years	5,568
After five years through ten years	3,316
Greater than ten years	4,239
Total	16,758	15,255
Residential mortgage-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	529
Amortized Cost	529	567
Fair Value
Debt securities, maturity, without single maturity date	554
Total	554	577
Commercial mortgage-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	645
Amortized Cost	645	594
Fair Value
Debt securities, maturity, without single maturity date	701
Total	701	605
Other asset-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	1,348
Amortized Cost	1,348	1,097
Fair Value
Debt securities, maturity, without single maturity date	1,358
Total	$ 1,358	$ 1,085

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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