Available-for-Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	$ 12,714	$ 12,341
Available-for-sale securities, gross unrealized gains	59	154
Available-for-sale securities, gross unrealized losses	(184)	(107)
Available-for-sale securities, fair value	12,589	12,388
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	12,681	12,308
Available-for-sale securities, gross unrealized gains	59	154
Available-for-sale securities, gross unrealized losses	(183)	(107)
Available-for-sale securities, fair value	12,557	12,355
Agency Mortgage-Backed Securities and CMOs [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	11,888	11,156
Available-for-sale securities, gross unrealized gains	41	113
Available-for-sale securities, gross unrealized losses	(166)	(105)
Available-for-sale securities, fair value	11,763	11,164
Agency Debentures [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	551	620
Available-for-sale securities, gross unrealized gains	18	28
Available-for-sale securities, gross unrealized losses	(12)	0
Available-for-sale securities, fair value	557	648
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	147
Available-for-sale securities, gross unrealized gains	0
Available-for-sale securities, gross unrealized losses	(4)
Available-for-sale securities, fair value	143
Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	55	487
Available-for-sale securities, gross unrealized gains	0	12
Available-for-sale securities, gross unrealized losses	0	0
Available-for-sale securities, fair value	55	499
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	35	40
Available-for-sale securities, gross unrealized gains	0	1
Available-for-sale securities, gross unrealized losses	0	(1)
Available-for-sale securities, fair value	35	40
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	5	5
Available-for-sale securities, gross unrealized losses	(1)	(1)
Available-for-sale securities, fair value	4	4
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	33	33
Available-for-sale securities, gross unrealized losses	(1)
Available-for-sale securities, fair value	$ 32	$ 33

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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