Debt - Long-Term Debt Maturities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Maturities Of Long Term Debt [Line Items]
2013	$ 78.0
2014	1,551
2015	825
2016	1,078
2017	1,784
2018	1,192
2019	990
2020	456
2021	139
2022	10
Thereafter	1,003
Subtotal	9,106
Unamortized premiums (discounts), net	13
Total	9,119.0
Consolidated Entities [Member]
Maturities Of Long Term Debt [Line Items]
2013	30.0
2014	27
2015	25
2016	126
2017	4
2018	74
2019	2
2020	2
2021	2
2022	3
Thereafter	6
Subtotal	301
Unamortized premiums (discounts), net	1
Total	302.0
Consolidated Entities [Member] | Secured Mortgage Debt [Member]
Maturities Of Long Term Debt [Line Items]
2013	30.1
Wholly Owned [Member]
Maturities Of Long Term Debt [Line Items]
2013	48.0
2014	1,524
2015	800
2016	952
2017	1,780
2018	1,118
2019	988
2020	454
2021	137
2022	7
Thereafter	997
Subtotal	8,805
Unamortized premiums (discounts), net	12
Total	8,817.0
Wholly Owned [Member] | Senior notes [Member]
Maturities Of Long Term Debt [Line Items]
2014	574
2015	175
2016	641
2017	700
2018	862
2019	693
2020	444
Thereafter	850
Subtotal	4,939
Unamortized premiums (discounts), net	42
Total	4,981.0
Wholly Owned [Member] | Exchangeable Notes [Member]
Maturities Of Long Term Debt [Line Items]
2015	460
Subtotal	460
Unamortized premiums (discounts), net	(63)
Total	397.0
Wholly Owned [Member] | Credit Facilities [Member]
Maturities Of Long Term Debt [Line Items]
2017	850
2018	142
Subtotal	992
Total	992.0
Wholly Owned [Member] | Other Debt [Member]
Maturities Of Long Term Debt [Line Items]
2014	659
2015	1
2016	1
2017	1
2018	1
2019	1
2020	1
Thereafter	10
Subtotal	675
Total	675.0
Wholly Owned [Member] | Secured Mortgage Debt [Member]
Maturities Of Long Term Debt [Line Items]
2013	48.0
2014	291
2015	164
2016	310
2017	229
2018	113
2019	294
2020	9
2021	137
2022	7
Thereafter	137
Subtotal	1,739
Unamortized premiums (discounts), net	33
Total	$ 1,772.0