Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt, due within one year	$ 9,920	$ 8,976
Long-term debt, due after one year	25,810	35,217
Total long-term debt	35,730	44,193
Trust preferred securities	2,600	2,600
Secured Debt	26,471	39,596
Unsecured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	3,044	1,663
Long-term debt, due after one year	9,049	10,444
Total long-term debt	12,093	12,107
Secured debt
Debt Instrument [Line Items]
Long-term debt, due within one year	6,876	7,313
Long-term debt, due after one year	16,761	24,773
Total long-term debt	23,637	32,086
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Secured Debt	$ 14,000	$ 14,900

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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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