Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Amortized Cost
Less than one year	$ 1,056
One year through five years	5,264
After five years through ten years	3,154
Greater than ten years	3,713
Total	15,588	$ 15,119
Fair Value
Less than one year	1,060
One year through five years	5,441
After five years through ten years	3,353
Greater than ten years	4,136
Total	16,469	15,255
Residential mortgage-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	542
Total	542	567
Fair Value
Debt securities, maturity, without single maturity date	564
Total	564	577
Commercial mortgage-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	612
Total	612	594
Fair Value
Debt securities, maturity, without single maturity date	658
Total	658	605
Other asset-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	1,247
Total	1,247	1,097
Fair Value
Debt securities, maturity, without single maturity date	1,257
Total	$ 1,257	$ 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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