Fair Value Measurements (Details 1) $ in Millions	Dec. 31, 2015 USD ($) stock	Dec. 31, 2014 USD ($) stock	Dec. 31, 2013 USD ($) stock
Perpetual preferred stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of stocks transferred from Level 2 to Level 1 | stock	5	14	15
Fair value of assets transferred from Level 2 to Level 1 | $	$ 19	$ 96	$ 70
Number of stocks transferred from Level 1 to Level 2 | stock	7	13	2
Fair value of assets transferred from Level 1 to Level 2 | $	$ 31	$ 83	$ 10
Common stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of stocks transferred from Level 2 to Level 1 | stock	7	0	2
Fair value of assets transferred from Level 2 to Level 1 | $	$ 80	$ 0	$ 35
Number of stocks transferred from Level 1 to Level 2 | stock	0	7	0
Fair value of assets transferred from Level 1 to Level 2 | $	$ 0	$ 26	$ 0
Redeemable preferred stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of stocks transferred from Level 2 to Level 1 | stock	2	1	3
Fair value of assets transferred from Level 2 to Level 1 | $	$ 11	$ 5	$ 21
Number of stocks transferred from Level 1 to Level 2 | stock	0	0	0
Fair value of assets transferred from Level 1 to Level 2 | $	$ 0	$ 0	$ 0