Contingencies and Commitments (Details) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2016 USD ($) agreement	Sep. 30, 2016 USD ($) agreement	Sep. 30, 2015 USD ($)
Guarantees Letters Of Credit [Abstract]
The range of expiration dates of guarantees made by the Parent Company			less than one year to more than 18 years
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 679	$ 679
No. of Agreements | agreement		40	40
Loss Contingency Accrual, Period Increase (Decrease)			$ 28	$ (91)
Guarantee Obligations [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 497	$ 497
No. of Agreements | agreement		17	17
Indemnification Agreement [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	[1]	$ 27	$ 27
No. of Agreements | agreement	[1]	1	1
Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 6	$ 6
No. of Agreements | agreement		15	15
Standby Letters of Credit [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 3	$ 3
No. of Agreements | agreement		1	1
Minimum [Member] | Guarantee Obligations [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 8	$ 8
Minimum [Member] | Indemnification Agreement [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss	[1]	27	27
Minimum [Member] | Standby Letters of Credit [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 3	3
Letter of credit fee percentage paid		0.20%
Maximum [Member] | Guarantee Obligations [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 58	58
Maximum [Member] | Indemnification Agreement [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss	[1]	27	27
Maximum [Member] | Standby Letters of Credit [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 3	3
Letter of credit fee percentage paid		2.50%
Unsecured Debt [Member] | Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 146	$ 146
No. of Agreements | agreement		6	6
Unsecured Debt [Member] | Minimum [Member] | Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 2	$ 2
Unsecured Debt [Member] | Maximum [Member] | Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		58	58
Secured Debt [Member] | Minimum [Member] | Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		1	1
Secured Debt [Member] | Maximum [Member] | Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 1	$ 1

[1] (1) Excludes normal and customary representations and warranties in agreements for the sale of assets (including ownership in associated legal entities) where the associated risk is considered to be nominal.