Investment Securities Noncredit impairment recognized in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Noncredit related impairment losses [Line Items]
Investment Income, Interest	$ 84	$ 48	$ 162	$ 95
Trading Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	1	1	1	1
Available-for-sale Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	78	41	149	83
Held-to-maturity Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	5	6	12	11
Taxable [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	74	42	143	84
Taxable [Member] | Trading Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	1	1	1	1
Taxable [Member] | Available-for-sale Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	71	38	137	78
Taxable [Member] | Held-to-maturity Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	2	3	5	5
Nontaxable [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	10	6	19	11
Nontaxable [Member] | Trading Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	0	0	0	0
Nontaxable [Member] | Available-for-sale Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	7	3	12	5
Nontaxable [Member] | Held-to-maturity Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	$ 3	$ 3	$ 7	$ 6