Investments (Available-For-Sale Securities By Contractual Maturities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities, Amortized Cost
Amortized cost	$ 87,267	$ 87,240
Available-for-sale Securities, Debt Maturities, Fair Value
Fair Value	92,059	95,086
Fixed maturity AFS securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost
Amortized cost	87,267	86,993
Available-for-sale Securities, Debt Maturities, Fair Value
Fair Value	92,059	$ 94,840
Fixed maturity AFS securities other than structured securities [Member] \| Fixed maturity AFS securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost
Due in one year or less	3,468
Due after one year through five years	18,142
Due after five years through ten years	16,434
Due after ten years	43,523
Amortized cost	81,567
Available-for-sale Securities, Debt Maturities, Fair Value
Due in one year or less	3,503
Due after one year through five years	18,473
Due after five years through ten years	16,626
Due after ten years	47,624
Fair Value	86,226
Structured securities [Member] \| Fixed maturity AFS securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost
Amortized cost	5,700
Available-for-sale Securities, Debt Maturities, Fair Value
Fair Value	$ 5,833

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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