Medium- And Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Federal Home Loan Bank, Advances, Weighted Average Interest Rate	0.92%
Potential future borrowings	$ 9,900
Pledged to the FHLB as collateral for potential future borrowings	5,500
Short-term Federal Home Loan Bank Advances	750
Long-term Federal Home Loan Bank Advances	3,800
Unamortized debt issuance cost	11	$ 12
Subsidiaries
Debt Instrument [Line Items]
Real estate-related loans securing FHLB advances	17,600
Long-term Federal Home Loan Bank Advances	$ 3,800	3,800
Floating-rate based on FHLB auction rate due 2026 \| Subsidiaries
Debt Instrument [Line Items]
Weighted-average interest rate	0.72%
Long-term Federal Home Loan Bank Advances	$ 2,800	2,800
Floating-rate based on FHLB auction rate due 2028 \| Subsidiaries
Debt Instrument [Line Items]
Weighted-average interest rate	1.47%
Long-term Federal Home Loan Bank Advances	$ 1,000	$ 1,000
Debt Instrument, Maturity Date	Jan. 26, 2028
2.50% notes due 2024 \| Subsidiaries
Debt Instrument [Line Items]
Stated interest rate	2.50%	2.50%
Debt Instrument, Maturity Date	Jul. 23, 2024	Jul. 23, 2024
Minimum \| Floating-rate based on FHLB auction rate due 2026 \| Subsidiaries
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Mar. 04, 2026
Maximum \| Floating-rate based on FHLB auction rate due 2026 \| Subsidiaries
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	May 20, 2026

Short-term Federal Home Loan Bank Advances

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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- Definition

Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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- Definition

Weighted average interest rate on advances made and reported by Federal Home Loan Bank (FHLBank).

+ References

No definition available.

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- Definition

The fair value as of the balance sheet date of financial instruments and other positions owned by the entity and pledged to counterparties as collateral, including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities.

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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- Definition

Weighted average interest rate of long-term debt outstanding calculated at point in time.

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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