Investment Securities Noncredit impairment recognized in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Noncredit related impairment losses [Line Items]
Investment Income, Interest	$ 84	$ 49	$ 246	$ 143
Trading Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	1	1	2	1
Available-for-sale Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	78	43	227	126
Held-to-maturity Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	5	5	17	16
Taxable [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	75	43	218	126
Taxable [Member] | Trading Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	1	1	2	1
Taxable [Member] | Available-for-sale Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	72	40	209	118
Taxable [Member] | Held-to-maturity Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	2	2	7	7
Nontaxable [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	9	6	28	17
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	6	3	18	8
Nontaxable [Member] | Held-to-maturity Securities [Member]
Noncredit related impairment losses [Line Items]
Investment Income, Interest	$ 3	$ 3	$ 10	$ 9