Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Asset Derivatives	$ 281	$ 507
Derivative Asset		212
Gross Amounts of Recognized (Liabilities)	(407)	(407)
Other Investments and Other Liabilities | Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(366)	(327)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(66)	(147)
Derivative liabilities	(240)	(84)
Accrued Interest and Cash Collateral (Received)	(60)	(96)
Financial Collateral (Received)	(298)	(178)
Net amount, liabilities	(2)	(2)
Other Investments and Other Liabilities | Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Asset Derivatives	253	455
Gross Amounts Offset in the Statement of Financial Position, assets	214	352
Derivative Asset	127	212
Accrued Interest and Cash Collateral Pledged	88	109
Financial Collateral Pledged	11	65
Net Amount, assets	$ 28	$ 38