Variable Interest Entities - Variable Interests Held by Us and Our Maximum Exposure to Loss Rising From Our Involvements in Those VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Variable Interest Held Classified as Assets	$ 2,337	$ 2,331
Variable Interests Held Classified as Liabilities	257	268
Total Assets in Unconsolidated VIEs	5,003	4,997
Maximum Exposure to Loss	3,547	3,541
Structured note vehicles [Member]
Variable Interest Entity [Line Items]
Variable Interest Held Classified as Assets	1,803	1,803
Variable Interests Held Classified as Liabilities	7	6
Total Assets in Unconsolidated VIEs	3,020	3,019
Maximum Exposure to Loss	3,013	3,013
Limited partnership investments [Member]
Variable Interest Entity [Line Items]
Variable Interest Held Classified as Assets	420	412
Variable Interests Held Classified as Liabilities	250	262
Total Assets in Unconsolidated VIEs	1,571	1,566
Maximum Exposure to Loss	420	412
Refinancing SPE [Member]
Variable Interest Entity [Line Items]
Variable Interest Held Classified as Assets	114	116
Variable Interests Held Classified as Liabilities	0	0
Total Assets in Unconsolidated VIEs	412	412
Maximum Exposure to Loss	$ 114	$ 116