Fair Value Measurements (Details) - Recurring - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	$ 42,412	$ 44,658
Liabilities	1,961	1,577
Fair Value Of Securities Transferred Between Level 1 And Level 2	0
Derivative Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	782	434
Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	1,179	1,143
Investment Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	41,949	44,313
Derivative Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	463	345
Non-U.S. Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value Of Securities Transferred Between Level 1 And Level 2		12
Government and Agencies
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value Of Securities Transferred Between Level 1 And Level 2		50
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	241	188
Liabilities	0	0
Level 1 | Derivative Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Level 1 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Level 1 | Investment Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	241	188
Level 1 | Derivative Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	42,051	45,163
Liabilities	4,892	6,024
Level 2 | Derivative Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	3,713	4,880
Level 2 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	1,179	1,143
Level 2 | Investment Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	37,740	39,719
Level 2 | Derivative Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	4,311	5,444
Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	3,988	4,429
Liabilities	4	2
Level 3 | Derivative Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	4	2
Level 3 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Level 3 | Investment Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	3,967	4,406
Level 3 | Derivative Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	21	23
Level 3 | U.S. Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	3,407	240
Level 3 | Non-U.S. Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	688	3,399
Netting Adjustment
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	(3,869)	(5,121)
Liabilities	(2,935)	(4,449)
Netting Adjustment | Derivative Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	(2,935)	(4,449)
Netting Adjustment | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Liabilities	0	0
Netting Adjustment | Investment Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	0	0
Netting Adjustment | Derivative Assets
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets	$ (3,869)	$ (5,121)