Fair Value Measurements - Recurring (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Debt
US corporate	$ 22,899	$ 23,703
State and municipal	4,340	4,675
Residential mortgage-backed securities	984	1,692
Commercial mortgage-backed securities	2,405	3,063
Asset-backed	97	295
Corporate Non-US	867	1,016
Government Non-US	1,252	1,710
US government and federal agency	3,882	2,013
Equity
Trading	19	21
Available-for-sale	125	132
Derivative Assets	1,207	1,630
Assets Fair Value Disclosure	38,075	39,950
Liabilities
Derivative Liabilities	11	56
Other Liabilities	19	20
Liabilities Fair Value Disclosure	29	76
Cumulative gain (loss) adjustment for non performance risk	2	15
Fair Value, Inputs, Level 1
Debt
US corporate	0	0
State and municipal	0	0
Residential mortgage-backed securities	0	0
Commercial mortgage-backed securities	0	0
Asset-backed	0	0
Corporate Non-US	6	0
Government Non-US	14	0
US government and federal agency	0	0
Equity
Trading	19	21
Available-for-sale	100	108
Derivative Assets	0	0
Assets Fair Value Disclosure	138	129
Liabilities
Derivative Liabilities	0	0
Other Liabilities	0	0
Liabilities Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2
Debt
US corporate	19,853	20,659
State and municipal	4,259	4,560
Residential mortgage-backed securities	981	1,676
Commercial mortgage-backed securities	2,403	3,054
Asset-backed	59	172
Corporate Non-US	579	680
Government Non-US	1,238	1,708
US government and federal agency	3,573	1,747
Equity
Trading	0	0
Available-for-sale	14	15
Derivative Assets	7,465	8,981
Assets Fair Value Disclosure	40,425	43,252
Liabilities
Derivative Liabilities	4,382	4,218
Other Liabilities	19	20
Liabilities Fair Value Disclosure	4,401	4,238
Fair Value, Inputs, Level 3
Debt
US corporate	3,046	3,044
State and municipal	81	115
Residential mortgage-backed securities	2	16
Commercial mortgage-backed securities	1	9
Asset-backed	38	123
Corporate Non-US	282	336
Government Non-US	0	2
US government and federal agency	309	266
Equity
Trading	0	0
Available-for-sale	10	9
Derivative Assets	67	27
Assets Fair Value Disclosure	3,837	3,947
Liabilities
Derivative Liabilities	7	9
Other Liabilities	0	0
Liabilities Fair Value Disclosure	7	9
Netting Adjustment Including Collateral
Debt
US corporate	0	0
State and municipal	0	0
Residential mortgage-backed securities	0	0
Commercial mortgage-backed securities	0	0
Asset-backed	0	0
Corporate Non-US	0	0
Government Non-US	0	0
US government and federal agency	0	0
Equity
Trading	0	0
Available-for-sale	0	0
Derivative Assets	(6,325)	(7,378)
Assets Fair Value Disclosure	(6,325)	(7,378)
Liabilities
Derivative Liabilities	(4,378)	(4,171)
Other Liabilities	0	0
Liabilities Fair Value Disclosure	(4,378)	(4,171)
Fair Value Level 1 Transfer Level 2 [Member]
Debt
US corporate	$ 0	13
Government Non-US		$ 487