Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt, due within one year	$ 8,705	$ 9,219
Long-term debt, due after one year	20,471	24,808
Total long-term debt	29,176	34,027
Trust preferred securities	2,600	2,600
Secured Debt	19,146	25,773
Unsecured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	1,063	2,214
Long-term debt, due after one year	10,146	8,990
Total long-term debt	11,209	11,204
Secured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	7,642	7,005
Long-term debt, due after one year	10,325	15,818
Total long-term debt	17,967	22,823
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Secured Debt	$ 11,500	$ 13,300

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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