Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	$ 1,267
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis	9,056
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	9,641
Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost	19,636
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	7,153
Available for Sale at Fair value - Amortized cost	46,753	$ 38,882
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	1,281
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value	9,387
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value	10,416
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	22,762
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	7,275
Fixed maturity securities available-for-sale	$ 51,121	$ 39,992

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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