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	Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Variable Interest Held Classified as Assets	$ 2,256	$ 2,331
Variable Interests Held Classified as Liabilities	290	268
Total Assets in Unconsolidated VIEs	4,599	4,997
Maximum Exposure to Loss	3,466	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	3,023	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	453	412
Variable Interests Held Classified as Liabilities	283	262
Total Assets in Unconsolidated VIEs	1,576	1,566
Maximum Exposure to Loss	$ 453	412
Refinancing SPE [Member]
Variable Interest Entity [Line Items]
Variable Interest Held Classified as Assets		116
Variable Interests Held Classified as Liabilities		0
Total Assets in Unconsolidated VIEs		412
Maximum Exposure to Loss		$ 116